I believe the Bible clearly teaches the Reformed Doctrine of Perseverance of the Saints, which means that those who are saved will by no means lose their salvation, rather they will preserver until the end. In this post I will provide biblical reasons for thinking this is the case and I will provide a defense against reasons for not thinking that this is the case.
The Bible clearly teaches in many places that you cannot lose your salvation:
John 6:44 No one can come to me unless the Father who sent me draws him. And I will raise him up on the last day.
All those who are drawn and come to God will be raised up on the last day. The term last day in the context of John 6 refers to the resurrection of glory (John 6:40). Which leads me to the next verse:
John 6:40 For this is the will of my Father, that everyone who looks on the Son and believes in him should have eternal life, and I will raise him up on the last day."
John 10:28-29 28 I give them eternal life, and they will never perish, and no one will snatch them out of my hand. 29 My Father, who has given them to me, is greater than all, and no one is able to snatch them out of the Father's hand.
No one can snatch those who have salvation out of the Father's and the Son's hand.
Philippians 1:6 And I am sure of this, that he who began a good work in you will bring it to completion at the day of Jesus Christ.
Paul, the inspired apostle, here says that the believers who God has begun a good work in will in fact make it on the last day.
1 Corinthians 1:8 who will sustain you to the end, guiltless in the day of our Lord Jesus Christ.
Paul is saying that God will sustain believers until the end. Notice the word guiltless here. This is quite a stab at christian denominations and groups that say a believer can have guilt before God at any point.
Romans 8:28-30 28 And we know that for those who love God all things work together for good, for those who are called according to his purpose. 29 For those whom he foreknew he also predestined to be conformed to the image of his Son, in order that he might be the firstborn among many brothers. 30 And those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified.
All those who are justified are glorified. Justification in the context of Romans refers to a event in the when one first receives righteousness and hence salvation (Rom. 3:20-25; 4:1-13). Paul is saying here that those who receive justification will in fact be glorified on the last day and given the context we have no reason to think that this glorious chain of redemption can be broken. This is even more evident when one reads the proceeding context which stresses that nothing can seperate the elect or saved from the love of Christ (Rom. 8:31-39), which is another clear proof of the doctrine of perseverance of the saints.
Now what about the objections to this biblical doctrine?
Well the most common objection to this doctrine is surprisingly philosophical in orientation, it goes something like this:
P1: If I have experienced S who went to x:church, y:professed faith, and z:had works for a long time T and at a future time T1 ceased from doing x, y, and z then S has lost his salvation.
P2: I have experienced S who did x,y, and z for a long time T and at a future time T1 ceased from doing x,y, and z.
C: Therefore, S has lost his salvation
The problem with this argument is premise 1. Someone can cease from doing x, y, and z and could of never been saved to begin with. The presence of x, y, and z does not necessitate the presence of salvation because someone could have man made reasons and intentions for doing x,y, and z and people could not be aware of those intentions and reasons. But this in no way defeats perseverance of the saints because it states that one cannot lose their salvation which is wrought by God alone, but surely someone can for other reasons stop performing x,y, and z.
Now lets take a look at the biblical arguments against this position:
I will respond to each of these arguments by what is called the Reformed covenantal view point, which is to say: People can loose their membership within the covenant community, but that the covenant community is not synonymous with ones salvation. For surely one can be in the covenant community and not have salvation (Romans (9:6).
Lets take this approach from a few of the supposed falling away passages:
Hebrews 10:29-31 29 How much worse punishment, do you think, will be deserved by the one who has spurned the Son of God, and has profaned the blood of the covenant by which he was sanctified, and has outraged the Spirit of grace? 30 For we know him who said, "Vengeance is mine; I will repay." And again, "The Lord will judge his people." 31 It is a fearful thing to fall into the hands of the living God.
This verse is teaching that if one falls away from the covenant community permanently that they will obtain more guilt than had they not been in the covenant community.
This verse would be teaching the same:
Hebrews 6:4-9 4 For it is impossible to restore again to repentance those who have once been enlightened, who have tasted the heavenly gift, and have shared in the Holy Spirit, 5 and have tasted the goodness of the word of God and the powers of the age to come, 6 if they then fall away, since they are crucifying once again the Son of God to their own harm and holding him up to contempt. 7 For land that has drunk the rain that often falls on it, and produces a crop useful to those for whose sake it is cultivated, receives a blessing from God. 8 But if it bears thorns and thistles, it is worthless and near to being cursed, and its end is to be burned. 9 Though we speak in this way, yet in your case, beloved, we feel sure of better things- things that belong to salvation.
John 15 would also be teaching this as well:
John 15:1-2 "I am the true vine, and my Father is the vinedresser. 2 Every branch of mine that does not bear fruit he takes away, and every branch that does bear fruit he prunes, that it may bear more fruit.
This verse teaches that those who do not produce fruit in the covenant community will eventually be cut off and this is made evident by them not producing x, y, and z.
Romans 11:17-22 17 But if some of the branches were broken off, and you, although a wild olive shoot, were grafted in among the others and now share in the nourishing root of the olive tree, 18 do not be arrogant toward the branches. If you are, remember it is not you who support the root, but the root that supports you. 19 Then you will say, "Branches were broken off so that I might be grafted in." 20 That is true. They were broken off because of their unbelief, but you stand fast through faith. So do not become proud, but stand in awe. 21 For if God did not spare the natural branches, neither will he spare you. 22 Note then the kindness and the severity of God: severity toward those who have fallen, but God's kindness to you, provided you continue in his kindness. Otherwise you too will be cut off.
This verse teaches that the Jews were cut off from the covenant community and that if the gentiles do not continue in the faith then there will be some day in which they are cut off from the covenant community. But you might say "well if one being in the covenant community is dependent on faith then how can you avoid the fact that this passages is referring to ones loss of individual salvation". My response to this is that a gentile parent could baptize their child in the covenant community and then their child could have never believed in the first place but stayed in the covenant community and then that unbelieving parent had children and baptized them out of tradition and then the children of that parent has no Godly influence and thus remains a non-believer and this could continue on until the entire cooperate unit would be cut off covenantally. In this way you can have a sort of cooperate breaking off of the covenant community without it effecting one's individual salvation.
Thus, given the covenantal understanding of these verses and the strong passages we have in support of perseverance of the saint we have to conclude that the answer to the question of whether or not one can lose their salvation has to be a confident No.