Since I have become more interested in evangelism in real life with real life people, I have been thinking quite a bit about talking faith with people who self-identify as atheists. If this is something you struggle with, there are some good tips here and here.
First, we must pray for them. When we pray, we acknowledge that we rely on the Lord’s power. We must not be confident in our own brilliance (Philippians 3:3); it is the Holy Spirit who draws people to Jesus (John 16:7-11; 12:32).
Second, we must speak the truth in love, treating atheists with gentleness and respect (Ephesians 4:15; 1 Peter 3:15). When we witness to others, we are not trying to win debates; rather, we are trying to lead them to Christ.
Third, don’t try to prove God’s existence beyond all reasonable doubt. Though this can be done, the goal is often too lofty. Our goal should be more modest: argue that theism (belief in God) is more reasonable than atheism (the rejection of belief in God).
Discuss common aspects of human experience–aspects accepted by both atheists and theists. Then argue that theism is a more reasonable explanation than atheism. Both sides agree that the universe had a beginning. It seems more reasonable to conclude that something outside the universe (i.e., God) caused it to exist than to believe that the universe popped into existence totally out of nothing and without a cause.
The caveat here is that this advice, or any advice you can find anywhere on the topic for that matter, only applies if you are talking to a reasonable person who is willing to have an honest and rational discussion, as the atheist at the second link was.
If you are talking to an online atheist, you should pray for them and end it there because the vast, vast majority of them only engage with Christians to stir up trouble.
They will tell you that they just have questions, that they just want to understand how Christians think, and that they just want to discuss matters of faith rationally and like adults. None of that is true, at all.
Truth is, evangelical online atheists, no matter how friendly and congenial they may appear at first, do not visit Christian blogs to play nice. They think Christians are delusional and crazy and that all non-believers have a civic duty (I would say higher calling but I think the irony would be lost on them) to protect society from our “mindnumbing BS.”
I took me a while to learn this lesson but I have come to the conclusion that consistently engaging with online atheists who troll Christian blogs deliberately and with malice of forethought is reprehensible, probably sinful, and a horrible look for God’s people.
“Do not answer a fool according to his folly, or you yourself will be just like him.“
– Proverbs 26:4