4 No one takes this honor upon himself; he must be called by God, just as Aaron was.
5 So Christ also did not take upon himself the glory of becoming a high priest. But God said to him, “You are my Son; today I have become your Father. ”
6 And he says in another place, “You are a priest forever, in the order of Melchizedek.” (Heb 5:4-6)

Sermon main points
1. High priesthood is an honour
2. High priests are called by God
3. High priest Aaron was called by God
4. High priest Jesus was called by God