Leviticus 16:32

And the priest who is anointed, and who hath offered his oblation to minister instead of his father, shall be clothed in the robes of fine linen, even the consecrated robes.

the kohen will perform atonement Scripture now returns to the previous discussion, explaining over what the kohen performs atonement.

anointed the one who is anointed with the anointing-oil, after being consecrated

wearing the one who wears these holy garments — for no one else may wear them

AND THE PRIEST WHO SHALL BE ANOINTED AND WHO SHALL BE CONSECRATED TO BE PRIEST IN HIS FATHER’S STEAD. “I might think that only [the High Priest] who has been anointed with the oil of anointment [may perform the Service on the Day of Atonement]. Whence do I know that a High Priest who is [inducted into office only] by many garments [i.e., the eight garments which distinguish him from all ordinary priests who wear only four garments, that he too may perform the Service on that day]? Scripture therefore says, and who shall be consecrated, by attiring the [eight] garments. Such were all the High Priests who functioned after the days of King Josiah [until the destruction of the Second Temple], for in his days the flask of anointing oil was hidden.”). This is Rashi’s language. Now the Rabbi did not intend to say that it was only from the days of King Josiah that there were High Priests who were [inducted into office only by means of] many garments, for in the Gemara we find that the Rabbis have said: “Who has precedence over whom [in being redeemed from captivity, etc.], a High Priest anointed with the oil of anointment, or one who was [inducted into office only] by his attiring himself in the many garments?” Again the Rabbis have said: “Does he [that killed a person unwittingly] return from the city of refuge [only] at the death of all of them [i.e., the High Priest anointed with the oil of anointment, and the one that was inducted into office only by his attiring himself in the many garments and one that had passed from his High-priesthood], or does he return at the death of one of them?” [Thus it is clear] that they can all be found at one time. Rather, [Rashi’s intent was that] if at any time [i.e., even when High Priests were still anointed with the oil of anointment], a priest was inducted [into the High-priesthood] by the many garments [worn by the High Priest], he was eligible to perform the Service of the Day of Atonement. For another priest was always prepared [in the High Priest’s stead] for the Day of Atonement, and he was not anointed. Thus if some disqualification occurred to the High Priest [such as by becoming impure etc.], this priest served in his stead, as he was eligible to do so through his induction [to his position] by his attiring himself in the many garments, even if he was not anointed.

וכפר הכהן אשר ימשח אותו, seeing that the Torah had previously stated that the service on the Day of Atonement is to be performed by the High Priest, i.e. בזאת יבא אהרן אל , הקודש, the Torah had to make provision for an alternate to Aaron if he or the High Priest in his generation was not available. The priest who had been anointed as an alternate would then officiate.

ואשר ימלא את ידו...ולבש, also a priest wearing the High Priest’s garments though not having been anointed with the holy anointing oil may be the instrument of the people’s atonement. [The conditions mentioned in our verse are not understood as cumulative and absolute requirements. (compare Rashi who explains that the holy anointing oil ran out already in the days of King Yoshiyahu during the first Temple, never to become available again. Nonetheless, even in the days of the second Temple, when the red cord turned white after the killing of the scape-goat, there was a sign from heaven that the people had been forgiven. Ed.]