Some believe Melchizedek was a ordinary man. Others believe he was the Lord himself. I don’t know nor do I think it is necessary to know. The book of Hebrews was written to Jews, and for the Jews the priests had to be from the tribe of Levi. Jesus was from the tribe of Judah. That could be a problem for the Jews to receive him as their high priest.
Hebrews 4:14 clearly says that Jesus is our great high priest that passed to the heavens! So how do we reconcile the difference?
Hebrews 7:16-17 says this, “Jesus became a priest, not by meeting the physical requirement of belonging to the tribe of Levi, but by the power of a life that cannot be destroyed." And the psalmist pointed this out when he prophesied, “You are a priest forever in the order of Melchizedek.” NLT
Jesus is far greater a priest than any Levite priest. All the Levite priests died, but our great high priest lives for ever. Romans 8:34, speaking of Jesus says, “who is even at the right hand of God, who also makes intercession for us.” Praise God we have Jesus literally at the right hand of God pleading for us !!!