Attended a funeral once where the preacher did a 10 minute rant on the need to tithe. Although he did have the decency not to pass the plate at the funeral itself.
There’s a time and place for everything. A funeral, where it is probable people of all backgrounds and religions are present, is not the place for a doctrinal sermon. Giving one strikes me as exhibitionistic.
A funeral is exactly the place for a doctrinal sermon. A chance to not just be preaching to the choir. A place to talk of the law and share the gospel. The format is determined by the denomination. In some the service is about the dead person. In others the service is about God and his plan for salvation. The sermon at my uncles funeral started with” Floyd was never known to darken the door of a church, and we have no reason to assume he is in heaven today.” We, the family, picked the church and the pastor and approved of that heartbreaking sermon. We could have had a eulogy at the funeral home but chose this on purpose. At least two people heard the gospel and were converted that I know of. My dad one of the two.