The Ordination of Aaron and His Sons
Hebrews does not leave us guessing whether Aaron matters for understanding Jesus' priesthood. It explicitly names Aaron's calling and then contrasts the whole mortal Aaronic order with Christ's permanent priesthood. Leviticus 8 is the concrete installation scene behind that argument.
Where this fits in the story: Exodus 28 — certain/explicit instruction → execution. The garments designed for Aaron and his sons are put on them here.
Where Scripture takes it next: Hebrews 5:1–6 — very strong inspired interpretation. Priestly honor is not self-appointed; Hebrews explicitly invokes Aaron as the comparison for divine calling.