In John 11, Lazarus would not have come out of the tomb if Jesus hadn’t called him, but Lazarus had a choice. He didn’t have to come out. He chose to obey the command of God. It’s the same way with salvation.
The Bible says, “In this is love, not that we loved God, but that He loved us and sent His Son to be the propitiation for our sins” (1 John 4:10). I think it was James Boice who used this illustration: If you put a bale of hay in front of a lion, is the lion going to eat that hay? There’s nothing keeping the lion from eating it, but never in a thousand years will the lion eat that hay because it’s not in his nature. He’s a carnivore by nature, and carnivores will never choose hay. It’s the same way with us. Anybody’s free to put his to trust in Christ, but the unsaved person will never choose to do it unless God does a work in his life. It’s only when we’re regenerated that we have the ability.
Now, you can go to extremes on either side of that. As somebody has said, try to explain predestination and you’ll lose your mind; explain it away and you’ll lose your soul. What I know is this: I never would have chosen Christ unless God had given me the ability to do that. Salvation is all of God. That doesn’t mean we don’t have a responsibility. We have to answer the call, and we’re to go and share that news with as many people as possible. But our spiritual rebirth started with God, not with us.