These days almost every religion allows cremation except for Orthodox Jewish, Islamic, Eastern Orthodox and someFundamentalist Christian faiths. The Catholic Church accepts cremation unless it is chosen for reasons which run against the Christian faith
Most Protestant Churches will allow the urn to be in the sanctuary during the service. A lot of Catholic Churches also allow the cremated remains to be present during the Memorial Mass. If the family is going to have a memorial service, the cremation urn should be present as it provides a focal point for the service.
While a cremation urn is not required by law an urn is usually desired when there is to be a memorial service or the remains are to be interred in a cemetery.