Take a few minutes to find out what Biblical Christianity teaches on that good question in the links of my signature. A man in the N.T. asked a very similar question.
A non believer may know what Christianity teaches, may have read the bible, but is not convinced....what then?
God is omniscient, meaning that he knows everything, past, present, and future. He knows what your final decision will be even if you waver back and forth for 50 years. Jesus said that God calls those who will be saved and those are drawn to him. So how does God know who to call? In Romans 8, it says that those who God foreknows will be called. That means that he knows whether you will chose for him or not. It's not predestination. You still have free choice, but God knows what that choice will be. With that knowledge in advance, he either calls you or he doesn't. The Bible doesn't say when that call will come. It could have already come and you're a work in motion, or maybe it won't come until you're on your deathbed. If you don't get called, don't say that God rejected you. You rejected him and he just knows it before you do.
“In a time of deceit telling the truth is a revolutionary act.” ― George Orwell
It's not over when you lose. It's over when you quit.
