There are quite a few Bible verses that explain what Reformed theology calls the perseverance/preservation of the saints (the P in TULIP). For example, you can read Jeremiah 32:40, John 6:35-40, John 10:28, Romans 8:30-39, 1 Thessalonians 5:23-24, and Jude 1:24-25 (etc.) to learn that those whom the Father loves, whom Jesus died for, and whom the Spirit renews will be kept by the Lord forever. But there is more biblical foundation to the doctrine of the perseverance of the saints than a handful of proof texts. Reformed theology also explains this doctrine using biblical logic and reasoning. Thomas Watson is a good example of this. In the quotes below, I’ve summarized some of his biblical arguments for the perseverance of the saints. Perseverance of the saints can be argued:
1) A veritate Dei – from the truth of God. God has promised and asserted that he will keep his people. God will so love his people that he will not forsake them; they shall so fear him, that they shall not forsake him.
2) A potentia Dei – from the power of God. By his sovereign power, God keeps his people. It is the power of God that keeps his people in the faith. We are not kept by our own power.
3) Ab electione – from God’s electing love. Those whom God has chosen before the foundation of the world will not be cast aside. God has loved them with an electing, everlasting love. Therefore God’s people will never fall away. No one can frustrate his purpose in election.
4) Ab unione cum Christo – from believers’ union with Christ. Those who are truly united to Christ will never be severed from him. The union is unbreakable.
5) Ab emptione – from the nature of a purchase. That is, Christ’s atonement was not potential; it wasn’t imperfect or incomplete but actual, perfect, and complete. Therefore, those whom Christ died for are saved forever. Christ will not lose those whom he has purchased.
6) A victoria supra mundum – from a believer’s victory over the world. Though the Christian might lose a battle here and there, the war has been one by Christ. Therefore saints overcome the world in Christ.
Of course there are Bible verses that come to mind when reading these six arguments. There are also other arguments to consider: 1) Those who are called, given new life, and sealed by the Holy Spirit cannot be uncalled, sent back into death, and be unsealed, 2) Those who are justified cannot be unjustified, 3) Those who are adopted can never be unadopted, 4) Those sheep for whom Christ intercedes will be kept by his intercession, and 5) The names written in the book of life will never be erased. Or, still another way to say it is that the doctrines of grace (TULIP) all go hand in hand.
Proof texting (in the proper sense of the term) is very helpful when considering the perseverance/preservation of the saints (along with other doctrines). However, we should also root our theology and doctrine in biblically based arguments. This helps Christians see that these doctrines are rooted in the fabric of Scripture and the story of salvation by grace alone.
Watson’s section on the perseverance of the saints is found on pages 280-282 of A Body of Divinity.