Leviticus 16:3 Commentary - Ellicott's Commentary for English Readers (Old and New Testaments)

(3) Thus shall Aaron come.—Better, With this shall, &c, that is, with the following sacrifices, ritual, vestments, &c, shall he approach the most holy place, after having offered previously the daily morning sacrifice, and performed the ordinary daily service. During the performance of the morning service the high priest, at the time of Christ, wore the golden vestments. These he changed for the white garments before he commenced the special ritual prescribed for this day.

With a young bullock for a sin offering.—Which had to be of the second year (see Exo. 29:1), and which the high priest had to buy with his own money. It was to be his own property because the victim was to expiate his own sins, since he, like the meanest sinner, required Divine mercy and forgiveness, though, owing to his high office, he had to bring a more costly sacrifice.