There are many things we're told to do and not do as Christians. But two in particular I want to stress are:
- We are to love and pray for everyone. This includes friends and enemies; believers and non-believers. We aren't allowed to pick and choose who we choose to love, or for whom we choose to pray.
But I say to you, Love your enemies and pray for those who persecute you (Matthew 5:44)
- Only God can see into the hearts of man. Yes, we tend to assume a lot. We see someone living a godless life, we assume they are godless. We hear someone confess they are a Christian, we assume they are Christian. But we cannot truly see what is in their hearts.
So he said to them, “You are those who justify yourselves in the sight of others; but God knows your hearts... (Luke 16:15)
Rest in Peace
These three words (or five if you go with the lengthy version "may he rest in peace") is essentially a prayer. We say these words to prayerfully request the person's soul goes to Heaven. We, as Christians, should want all people to go there. We should be praying for the souls of all - friends and enemies. Those who stand by us and those who persecute us. Those who believe in the Lord, and those who don't yet.
As I said before, we aren't supposed to be picking and choosing who to pray for. Yes, I may not think someone is a Christian. He's a sinner. He has perhaps even actively stated there is no God. Is this not more reason to pray for his soul?
And, as I also stated before, I can't truly see into his heart. True, someone who would state aloud "there is no God!" quite probably is not Christian. But I do not with 100% certainty know this to be true. And I cannot know with 100% certainty if this person's soul is saved. All I can do is pray for him.
That is all any of us can and should be doing - pray for everyone. Pray while they're alive that they are able to find Christ. And pray when they die a request that their soul may rest in peace.