the p-word

John Piper in Bloodlines on perseverance:

Perseverance simply means that those whom God calls, he keeps. If you are a true believer, you will persevere in faith and (imperfect) obedience to the end and be saved. God will see to it. “Those whom he predestined he also called, and those whom he called he also justified, and those whom he justified he also glorified” (Rom. 8:30). Between justification and glorification, no one drops out. All persevere from justification to glorification.

Jesus said, “My sheep hear my voice, and I know them, and they follow me. I give them eternal life, and they will never perish, and no one will snatch them out of my hand” (John 10:27–29). Paul said, “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” (Phil. 1:6; see 1 Cor. 1:8; 1 Thess. 5:23). If someone leaves the faith, it was because they never truly belonged to Christ. This is the way the apostle John described that situation in his day: “They went out from us, but they were not of us; for if they had been of us, they would have continued with us. But they went out, that it might become plain that they all are not of us” (1 John 2:19).