Some translations set poetry farther to the right than the rest of the text to show that it is poetry. The ULB does this with the poetry in 7:17, 21, which is from the Old Testament.
Only a high priest could offer sacrifices so that God could forgive sins, so Jesus had to be a high priest. The law of Moses commanded that the high priest be from the tribe of Levi, but Jesus was from the tribe of Judah. God made him a priest like the priest Melchizedek, who lived at the time of Abraham, before there was a tribe of Levi.
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