Shem lived long after the death of Abraham. And wouldn’t it make sense he is the Priest since he’s the oldest male of the Semite family? One Jewish story is when Rebekah goes to inquire about the twins in her womb she goes to Shem.
I just find it fascinating and a little mind blowing. A Centurian? A Roman officer, a follower of Christ before He died on the cross. How did he meet Christ? How did he know of his teachings?
Something must have happened, an interaction, did Christ carry his pack two miles instead of one? Imagine the conversation and the conversion, Christ walking with a Centurian, talking to him, the religion of the Jews a complete pile of nonsense to a tough Roman officer.
Really, something happened that we know nothing about for this Roman to be a follower of Christ well before He rose from the dead.
I take no credit at the theory of Christ carrying the officers pack two miles, that is from a personal conversation with my priest who also finds this man so interesting and a mystery.