In Christianity, it is believed that on "Judgement Day" Jesus would come alive and will give life to all noble people who are already dead and all evil people will remain dead. So Christians bury their loved ones with a hope that Jesus will bring them alive on Judgement Day. Until then they ask them to “Rest in Peace”.
In Hinduism, ultimate goal for any soul is to attain Moksha, meaning to unite with God and not take rebirth. But to attain Moksha you should not have any balance of Punyam or Paapam. If you leave body with Punyam or Paapam you will be born again to spend the balance of your Paapam or Punyam. That’s why they say - Punaraapi jananam Punaraapi maranam. One would never know if they are leaving with balance of Punyam or Paapam. But relatives wish them "Om Shanti" that is to not be reborn again and attain eternal peace by joining the abode of God.
