I would now like to address the question as to whether a Christian has eternal security. A key Scripture in this discussion is John 10:27-29 where Jesus said: My sheep hear my voice, and I know them, and they follow me: And I give unto them eternal life; and they shall never perish, neither shall any man pluck them out of my hand. My Father, which gave them me, is greater than all; and no man is able to pluck them out of my Father's hand.
Many have erred in interpretation of this Scripture. There are two extremes, those who claim more security than the Scripture says, and those who teach less.
Firstly regarding those who claim more security than the Scripture says. These say that those who believe the doctrines of the bible are God's sheep, and have eternal security whatever they do. But although the context of this Scripture is of belief, Jesus says that only those who hear His voice and follow Him are His sheep. This means obedience. So those who do not obey Christ are not His sheep, and this promise of security does not apply to them.
Secondly there are those who undermine the security promised. They interpret the Scripture as if it were a conditional promise with an extra ‘if’. I will point out their error by misquoting the verse the way they interpret it – ‘if my sheep hear my voice they shall never perish.’ But Jesus did not say this. He made two independent statements: His sheep hear His voice; and His sheep are secure.
But what if one of God's sheep stops listening to His voice? The teaching here is that this does not generally happen, as Christ said: My sheep hear my voice. And if it does happen, Christ taught in a parable of Luke 15:11-32 that He is able to rescue the lost sheep. But does it ever happen that a sheep refuses to be rescued?
One Scripture that is relevant in answering this question is Romans 5:9,10: Much more then, being now justified by his blood, we shall be saved from wrath through him. For if, when we were enemies, we were reconciled to God by the death of his Son, much more, being reconciled, we shall be saved by his life. So if it is easier for God to keep a Christian faithful than to convert him, Christians may have confidence that they will be kept faithful by God.
God's part in upholding us in faithfulness is spoken of in Jude 24,25: Now unto him that is able to keep you from falling, and to present you faultless before the presence of his glory with exceeding joy, to the only wise God our Saviour.
But while we have these promises of God's keeping power it also should not be forgotten that we have a part in keeping ourselves faithful to God, which is spoken of in Jude 20,21: But ye, beloved, building up yourselves on your most holy faith, praying in the Holy Ghost, keep yourselves in the love of God, looking for the mercy of our Lord Jesus Christ unto eternal life.
If we do not keep ourselves in the love of God by obedience and prayer, the word of God is severe for Paul says: Behold therefore the goodness and severity of God: on them which fell, severity; but toward thee, goodness, if thou continue in His goodness: otherwise thou also shalt be cut off. (Romans 11:22) Falling in this context does not mean committing one sin but completely turning away from God permanently by continuing in sin.
God says that if we turn away from Him we will be cut off if we fail to return to Him. But God does not say that there will be those who do this. If there are some that are cut off , Jesus' assurance of John 10:27-29, that His sheep hear His voice and are secure, is fairly meaningless. Also the reason for this, stated in Romans 5:9,10, that it is easier to keep a Christian than to convert him, would be false.
There are, however, those who wrongly assume they are born again, and become carelessly disobedient. But if these would apply their hearts unto obedience, they would eventually receive the Spirit's gift, because they then would be Jesus' sheep.
So what should be our attitude of mind regarding our security? Firstly because of the assurances of God's keeping power we should not be so insecure of our destiny that we fail to: rejoice, because your names are written in heaven. (Luke 10:20) Secondly we should not be so confident of our security that we ignore God. So Paul says in Romans 11:20: Be not highminded, but fear. Therefore we should watch and pray. But if we have the right attitude of reverence for God's word and carefulness we can say with Paul: I know whom I have believed, and am persuaded that he is able to keep that which I have committed unto him against that day. (2 Timothy 1:12)