Well, when ppl say "r.i.p." they are referring to the soul, and if they haven't obeyed the gospel, they're soul isn't going to be resting in peace on from the day they die to eternity - And I heard a loud voice from heaven saying, “Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people. God Himself will be with them and be their God. And God will wipe away every tear from their eyes; there shall be no more death, nor sorrow, nor crying. There shall be no more pain, for the former things have passed away.” He who overcomes shall inherit all things, and I will be his God and he shall be My son. But the cowardly, unbelieving, abominable, murderers, sexually immoral, sorcerers, idolaters, and all liars shall have their part in the lake which burns with fire and brimstone, which is the second death.” (‭Revelation‬ ‭21‬:‭3-4, 7-8‬ NKJV)

I love the way you wrote this. I pretty much agree with everything you said. My favorite part is the last few lines about how we only say that so we don't feel bad burying our friends.

That's just the body. What about the soul? I think that's what they mean by Rest in Peace. :) just a guess though.