Q. For Christians, is cremation an accepted form of the disposition of a person’s final remains, or is it a sin? What if you are a Christian living in a land-scarce country or city and cremation is the preferred method?
As far as I know, the Bible does not comment specifically on cremation. The preferred practice within the believing communities of both the Old Testament and the New Testament was burial. It was considered an insult and a sacrilege to leave a body exposed without burial, and the Law of Moses forbade doing that beyond sundown on the day a person died.
But this does not mean that cremation was unknown to those communities. For example, it was widely practiced within the Roman Empire until, interestingly, over a couple of centuries the influence of Christians and other groups with a strong belief in the afterlife changed the preference to burial. So one observation we can make is that the New Testament writers knew about cremation, and so if they had wished to condemn the practice, they could have, as they do condemn other cultural practices that they deem unacceptable.
But I think the most useful observation is that the Scriptures know (if I could personify them, as the biblical writers themselves do) that not everyone has the opportunity to be buried. For example, some people might be lost at sea when a ship sinks. That is why, I believe, the book of Revelation, envisioning the Last Judgment, says, “The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what they had done.” (I take “death” and “Hades” here to be references to the underworld or abode of the dead, presumably of those who were buried.)
The bottom line, in other words, is that no matter what the disposition of a person’s final remains, everyone will be raised from the dead and judged appropriately, with hopefully many being welcomed into God’s presence for eternity.
This makes sense, because even a body that is buried completely decomposes after some time. It’s not as if buried bodies remain intact until the resurrection, while cremated bodies are incapable of resurrection. Either way, God must somehow reconstitute a body. We do not know exactly how that is done, but it seems not to depend on why the body needs to be reconstituted.
So I would say that cremation is an option that Christians may validly choose, perhaps for the reason you mentioned, to practice good stewardship of scarce land, and perhaps for further reasons as well.