"What does the Bible say about cremation? Is it wrong to cremate a believer's body?"
Reader should the believer be cremated?? Does the word say anything about how we should be laid to rest??? I grew up believing that a believer should not be cremated nor should they participate in organ donations.
The Bible does not give any specific teaching about cremation. There are occurrences in the Old Testament of people being burned to death (1 Kings 16:18; 2 Kings 21:6) and of human bones being burned (2 Kings 23:16-20), but these are not examples of cremation.
Anyhow Pastor John Piper gives two reasons for us to bury rather than burn our loved ones.