Everyone knows that God exists.
The fool hath said in his heart, There is no God. -- Psalm 14:1
There is no such thing as an atheist. Everyone knows that there is a God. The question is whether we recognize Him as Lord and obey His will for our lives, or whether we reject and rebel against Him. The atheist says that God does not exist, but God said atheists do not exist. Fools, however, do exist.
I stirred up a hornet's nest on Twitter last week when I said there are no atheists. One special snowflake even responded to me, and then immediately blocked me so I could not see his response. (Of course, I can see all responses to my tweet via private browsing!) That is a special kind of cowardice from someone who needs to immediately run to his safe space when reading a 280-character missive from someone he has never interacted with. I found it absolutely hilarious.
How do we know that there are no atheists? Because God tells us so in His Word. We know from Romans 1:18-25 that all mankind knows of God and that no one has an excuse for not believing. However, some refuse to glorify Him as God, and are given over to a depraved mind.
But you cannot use the Bible to prove itself, you might say. Well, yes, actually I can. The Bible enjoys a special status that no other book in human history has ever enjoyed, because it is the divinely inspired Word of God, sharper than any sword. It carries a special authority. As Christians, we should never shy away from appealing to Biblical authority in making an argument.
Doug Wilson said that there there are two primary beliefs of atheism: There is no God, and I hate Him. The blasphemy spewed against my Savior has demonstrated that to be true. I pray that God will soften atheists' hearts and call them to saving faith in His only begotten Son.