There are two types of Atheists.
- Atheist fundamentalists and 2) those who just don’t want to practice any religion.
The former will take every attempt to poke at your faith, try everything to convert you to their religion. They are quite pushy and loudmouthed.
The latter just don’t believe and are “live and let live” types.
If you are with the former, run away. You cannot reason with them or talk about anything without drama happening.
If you are with the latter, there’s nothing to worry about.
The existence of God is the first barrier.
If they’re open to it, and the topic comes up, you can mention Aquinas’ 5 proofs of the existence of God.
aquinasonline.com/Topics/5ways.html
Or Peter Kreeft’s writings:
peterkreeft.com/featured-writing.htm
peterkreeft.com/topics-more/20_arguments-gods-existence.htm
Or an interesting argument I heard (forgot what this argument is called)
Imagine all the knowledge in the universe. Draw a circle to represent this.
Imagine all the knowledge of mankind. Draw a circle inside the first one to represent this. Obviously it is smaller and 100% contained within the larger circle.
Imagine all the knowledge you have. Draw a circle inside the humanity’s circle. (I’m too humble, I’ll put a dot.)
In order to know there is no God, one must have all the knowledge of the universe (which we don’t have) - otherwise, what is more likely: knowledge of God’s existence is outside of your circle or outside of humanity’s circle? It can’t be outside the universe’s knowledge circle (this is logically impossible). Since we don’t have all the knowledge in the universe, it is quite arrogant to claim that there is no God since we don’t have the proof of this.
Once they believe in God, I’d invite them to download Fulton Sheen’s discussion of the Claimants. Here he goes one by one for all the claimants to have spoken for God and chops one at a time away until only Christ is left.