Some translations indent each line of poetry to make it easier to read. The ULB does this with the poetry in 7:17, 21, which is quoted from the OT.
Jesus’ role as high priest is explained in detail in this chapter. (See: rc://en/tw/dict/bible/kt/sin)
The high priest was normally from the tribe of Levi, but Jesus was from the ruling tribe, Judah. His right to be a priest came from the tradition of Melchizedek, who was a priest before the Levites came into existence. This passage will be difficult to understand if Genesis has not been translated first. (See: rc://en/ta/man/translate/figs-explicit)
The author mentions the New Covenant and discusses Jesus’ relationship to it. (See: rc://en/tw/dict/bible/kt/newcovenant)