This is a very controversial topic indeed! Be very careful what you believe about the doctrines you have been taught at church and elsewhere. Often, very sincere teachers share with us what they have been taught, and sometimes our teachers are mistaken. When it comes to understanding Bible doctrines, mistakes arise from (1) not considering all the evidence in the Bible that touches on the subject;  (2) leaving out vital evidence that, when understood, makes a great difference in how Bible truth should be expressed;  (3) failing to account for cultural factors that shed additional light on what the Bible records;  (4) failing to account for grammatical factors that more precisely define exactly what the Bible declares or promises; (5) bringing to the Bible a doctrinal framework that does not conform to what the Bible itself actually says or emphasizes. On Facebook my good friend Cris Jackson shared the following post on June 27, 2017:

ETERNAL SECURITY: Some think you can lose your salvation. Lets see the word of God says about this. (John 10) 27 "My sheep hear My voice, and I know them, and they follow Me: 28 And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of My hand. 29 My Father, which gave them Me, is greater than all; and no man is able to pluck them out of My Father's hand. 30 I and My Father are one." (Sounds very secure to me lets read on Ephesians 4:30) "And grieve not the holy Spirit of God, whereby ye are "sealed" unto the day of redemption." (Sounds very secured to me sealed lets read on Luke 8:13) "They on the rock are they, which, when they hear, receive the word with joy; and these have no root, which for a while believe, and in time of temptation fall away." (So the question is the person that fell away were they ever saved? 1 John 2:19) "They went out from us, but they were not of us; for if they had been of us, they would no doubt have continued with us: but they went out, that they might be made manifest that they were not all of us." Please read all comments below for more clear in-depth teaching. Also pray and ask God to show you the Spirit will testify. I did not understand it at first neither but Holy Spirit showed me and testified to it. God bless.

Cris Jackson followed the above opening comment with the following briefer comments:

John 6:37 All that the Father giveth me shall come to me; and him that cometh to me I will in no wise cast out. This great promise clearly teaches eternal security of the born again believer (John 17:2). Once Saved, Always Saved / Eternal Security For a Christian to lose salvation, he would have to be un-born again. 1 Peter 1:23 says “being born again... by the word of God.” You may disobey your earthly parents, but you are still their child. Likewise, you may disobey your heavenly Father, but you are still his child. For whatsoever is born of God overcometh the world: and this is the victory that overcometh the world, even our faith. (1 John 5:4)

Lastly, Cris Jackson cited the following from James L. Melton, The Bible Believer's Helpful Little Handbook:  A Handy Reference Guide for Plain Folks Like Us, pages 13-14

 Eternal Security The Eternal Security doctrine is the "once saved, always saved" doctrine that so many people have trouble believing because it just doesn't sound logical. Actually, it is VERY logical and very scriptural as well. My eternal security in Christ is based on my RELATIONSHIP with God, not my fellowship with Him. I am not saved because I fear God and serve Him, but rather because I have entered into a Father/Son relationship with Him through the Lord Jesus Christ. I was once a child of the Devil and a child of wrath (John 8:44; Eph. 2:3), but now I am a son of God (John 1:12; 1 John 3:2; Rom. 8:14; Gal. 4:5). Upon receiving Christ as my Saviour, I was SEALED with the Holy Spirit until the day of redemption (Eph. 4:30; 2 Cor. 1:22), and I am KEPT by the power of God (1 Pet. 1:5), not by my own power. Jesus will never leave me nor forsake me (Heb. 13:5; Mat. 28:20), because He BOUGHT me with His own blood (Acts 20:28; 1 Cor. 6:19-20). If I choose to be a disobedient child, then my Father in Heaven will CHASTEN me (Rev. 3:19; Heb. 12:4-8; 1 Cor. 11:30-32), but I will remain a saved and sealed son of God (John 5:24; 1 John 5:11-13; Rom. 8:38-39; Phil. 1:6; John 6:37; 10:28-29).

Here is my initial response on the discussion thread: " 'Once saved, always saved' is heresy. Unconditional eternal security is heresy. Of course, both are unbiblical in the extreme. What the Bible does teach is the absolute eternal security of the believer, not the unbeliever. Luke 8:13 clearly teaches that it is possible to stop believing. The moods and tenses in the Greek text of the New Testament are very clear on this matter. John 10:27 clearly specifies that the promise given in John 10:28 pertains to those who continue to hear His voice and continue to follow our Lord Jesus Christ. Anyone who practices the sins listed in 1 Corinthians 6:9, 10 will not inherit the Kingdom of God. In the Bible there is such a doctrine called 'apostasy.' That being the case (check your Bible; check Nave's Topical Bible to see a long listing of verses in the Bible declaring this doctrine), the unqualified assertion 'Once Saved, Always Saved' must be mistaken. For documentation of the relevant underlying Greek grammar, see the extensive notes in the Lavender's New Testament, a most valuable resource for getting these things correct!" Cris Jackson responded to me as follows: "Pastor Jerome Smith help me understand so is it in the wording. I want to make sure we are on the same page. What I have said in the above teaching is if you truly belong to Christ this will be evident. If you don't belong to Him even though you were in church but you left that will be evident as well. Also are you saying that it's possible for a believer to stop believing? What did Christ mean exactly when He said they cant be plucked out of His hand. What's the difference between eternal security and absolute security? They both sound the same to me just different words. Luke 8:13 the question is were they truly saved? Let me add I am not saying a person who practices sin has eternal security as most teach that is not what I am saying here." I replied: " If you truly belong to Christ, you will have experienced regenerative change (Titus 3:5; 2 Corinthians 5:17). You have become a new creature in Christ. You have become a new creation. The effect of the blood of Christ is far superior to the effect of the Levitical sacrifices in the Old Testament: Hebrews 10:4, 11 tells us that those Old Testament sacrifices could not take away or remove sin. The blood of our Lord Jesus Christ shed on the cross of Calvary has more power than those OT sacrifices did. It truly does remove or take away sin in this life. When we are saved, genuinely saved, we have a new nature. The Holy Spirit seals us, fills us, baptizes us (1 Corinthians 12:13; Ephesians 4:30; Ephesians 5:18). A truly saved person will not practice the sins named in 1 Corinthians 6:9, 10 and its parallel passages. A truly saved person may sin (1 John 2:1, 2), but if truly saved he or she will repent and ask for forgiveness. In Luke 8:13, Jesus specifically states that the persons described "believed for a while." That means they truly believed. But the "for a while" lets you know that those persons failed to continue to believe, for whatever reasons specified in the context: "in times of temptation [they] fall away." The contrast I am pointing out here is between "unconditional eternal security" (often expressed as "Once saved, always saved") and what I call "absolute eternal security" possessed by believers who continue to believe and obey the Gospel. When Jesus gave the promise in John 10:29 that "no one is able to pluck them out of my Father's hand" he has reference ONLY to those who meet the conditions specified in John 10:27, which specifies the kind of believers He has reference to: those who CONTINUE to hear His voice, and those who CONTINUE to follow Him. The necessary condition that we have a continuing faith is specified in the Greek text because this is the force of the present tense used here in the Greek. The concept includes the fact that such a person continues to obey. In John 10:28 a more accurate translation from the Greek text for the KJV "and they shall never perish" would properly read "and they MAY never perish." The MAY more accurately conveys the subjunctive mood of the Greek text at this point. The subjunctive mood states that there is a CONTINGENCY involved. The CONTINGENCY is what is stated in the preceding context at John 10:27, the necessity to continue hearing, continue obeying, continue following. What kind of "following" is Jesus talking about? A related verse helps clarify the issue. John 12:26 reads in the KJV, Joh 12:26 If any man serve me, let him follow me; and where I am, there shall also my servant be: if any man serve me, him will my Father honour. The expression "let him follow me" is more accurately translated from the Greek text to read "he must always follow Me" as in the Lavender's New Testament. The Greek construction here is called "the imperative of obligation," regarding which Dr. Lavender comments, "Pay attention to this powerful imperative of obligation, must always follow" (note h, page 179). Therefore, the promise of security applies only to those who continue to hear and continue to follow. Scripture asserts the absolute security of the believer, not the unbeliever. Where do I get the ABSOLUTE from? That is based on the very strongest negation in Greek that is possible to express when Jesus promised "they may never, never perish forever" in John 10:28." Cris Jackson responded:  Jerome Smith Pastor with all due respect we there is no way you can be a true believer and fall away Christ said His Father gave us to Him so if He loses us that means God messed up somewhere. I've taken all here and I'm going to let the Holy Spirit speak to me more about this as time goes on. I thank everyone for their comments and spiritual insight. My belief is you can't belong to Christ and he lose you. You can't belong to Christ and continue to sin. A change is going to happen. If a person has been in church for years and believe what they heard and fell away never to return this leads me back to that Scripture that they never was of us. Even if a person backslides the Lord is married to them. " I replied: "Cris Jackson, you need to go back and carefully read the FACTS and EVIDENCE I carefully marshaled from Scripture itself in my post answering your questions immediately above. Jesus Himself directly said there were some who "believed for a while." That means they truly believed. Jesus said they believed until the difficulties of the testing they experienced overwhelmed them and they "fell away." Falling away is a direct reference to the fact that they "became apostate," as expressed in the Friberg Greek Lexicon in defining the term used in Luke 8:13. In my own careful study of Scripture I have noted two kinds or categories of apostasy: (1) moral apostasy, such as the willful and continuing practice of sin as specified in 1 Corinthians 6:9, 10; (2) doctrinal apostasy, such as denying the deity of our Lord Jesus Christ as specified in John 8:24. You are mistaken in your thinking when you state "No way can you be a true believer and fall away. Christ said His Father gave us to Him SO IF HE LOSES US THAT MEANS GOD MESSED UP SOMEWHERE." No, it explicitly states that it is the individual who fails to meet the specified CONTINGENCY expressed by "MAY not perish" and defined in the preceding context as being the requirement to CONTINUE hearing and obeying, and CONTINUE following who messed up. There is NO WAY to successfully argue against the statements inspired by God Himself that are unquestionably present in the divinely inspired Greek text of the New Testament. In order to accurately understand the doctrine of Scripture you must understand the grammar of the Greek text that underlies our English translations of that text. I have carefully shared with you that understanding for the passages we have been considering." Cris Jackson replied, " Jerome Smith As I said I will take all that has been presented here and let the Holy Spirit do the rest as my Pastor always says if you think you can lose your salvation then you better hurry up and get it back " I replied: "Your pastor is right about that! I don't plan on losing mine. I am sure you don't plan on losing yours either! The issue is that true believers continue in their faith, as stated in Colossians 1:23. But we must continue to be "grounded and settled," and not "move away from the hope of the Gospel." Cris Jackson responded, " Jerome Smith you said the key word true believers there are those who believe that are not true and they fall away. I think the Scriptures say they are forever learning but never able to come to the full understanding of the truth... I will study what you have presented and let the Holy Spirit bring the clarity the seeds has been planted. " I responded:  "Now you see the point! But only if you truly understand that it is possible, though not usual or likely, that a person who truly believed came to a point in their life where they stopped believing, stopped obeying, and stopped following. Jesus said there are such persons. The Greek grammar states this is possible, so that is why warnings against falling away or apostasy are present in the New Testament. This shows why it is important that we obey Hebrews 3:12, 13. I obeyed that many years ago even as an English teacher, and you know one of the results. Heb 3:12 Take heed, brethren, lest there be in any of you an evil heart of unbelief, in departing from the living God. Heb 3:13 But exhort one another daily, while it is called To day; lest any of you be hardened through the deceitfulness of sin. Heb 3:14 For we are made partakers of Christ, if we hold the beginning of our confidence stedfast unto the end;" Cris Jackson replied: "Jerome Smith will that fall into line with this Scripture? (2 John 2:8) 7 For many deceivers have gone out into the world, refusing to confess the coming of Jesus Christ in the flesh. Any such person is the deceiver and the antichrist. Watch yourselves, that you do not lose what we have accomplished, but that you may receive a full reward. 9Anyone who runs ahead without remaining in the teaching of Christ does not have God. Whoever remains in His teaching has both the Father and the Son.…" I replied, "Cris Jackson, that is a perfect example of what I meant by the passages in the New Testament that warn against doctrinal apostasy." Cris Jackson responded with the following question: "Jerome Smith so what does this verse mean (John 10:28) "And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand." I answered, "John 10:28 means exactly what I explained it to mean in my comments above. Note particularly that the "shall" is a wrong translation of the Greek subjunctive mood here, so it should read "may not perish." May points to the preceding contingencies or requirements that must be met for the promise to each individual to hold true. If you continue to hear and obey, and continue to follow, then the promise of John 10:28 holds true and applies to you. If you do not continue to meet the contingency then the promise no longer is valid for you until you do." Cris Jackson responded, " Jerome Smith ok I got cha"   Notice particularly that my "argument" is based upon a strict grammatical exegesis of the verses involved in the discussion of Eternal Security. When we are careful to observe and account for then apply the significance of the subjunctive mood found in the Greek text of the New Testament, we arrive at an accurate understanding of what the truth conveyed in the New Testament declares about our security in Christ. May I express a special "Thank You" to Cris Jackson for bringing up such an important subject and for her allowing me to participate in her Facebook discussion.