Many Christians oppose cremation because they believe it devalues the body that will be raised on the last day. Of course, they agree that God can raise the body in whatever form it has been cast into the ground or the water or the mountainside. But a lot of people say that since the body will be raised rather than being destroyed by fire why should we burn the body now?
Furthermore, cremation has often been practiced in non-Christian cultures associated with all sorts of pagan rites to go against our biblical understanding of death and the resurrection. I was in India, Varanasi, the spiritual center of Hinduism, and just sat there marveling at the rituals and the demon possession of priests as they whirled around and chanted and then burned the bodies and sent them out into the water. So a lot of people say “we don't like those associations” will have nothing to do with it. Other believers say cremation is okay because it preserves the body as much, maybe even more than, burial in a casket.
The body disintegrates gradually anyway and turns to dust, so are dust and ashes really different? In any case, God is going to raise the same body to life immortal by his miraculous power and pagan rites have been associated with traditional burial too. A lot of people have been buried in the ground, their whole bodies and in caskets, with pagan rites. So the method of burial doesn't really make it pagan or Christian. Here's my view of the matter, my parents were cremated and I had no qualms at all about that and I'm happy to be cremated as well. My wife does have qualms about it. So it’s up to her.
I think it's a matter of personal preference and also conscience. That's very important, conscience. If you think you’re dishonoring the body by cremation then don't do it. If you believe you're simply burying the body in the form of ashes, you have Christian liberty to make that choice. There's nothing inherently pagan or disrespectful about it. I think we should all agree that Christian burial requires a proper service with a minister committing the body to the grave and the hope of the resurrection. But whether it's in the form of a jar of ashes or a casket really depends on the wishes of the family.
God can resurrect our bodies miraculously God can resurrect that same body from ashes spread out at sea or somebody who dies at sea and is eaten by sharks. God made our bodies miraculously, he can resurrect our bodies miraculously and he's promised to do that.
Adapted from an answer given in Episode 85 of the Core Christianity Radio Show.