The Self-Donation of God, pg. 50:
"Not only does the Old Testament suggest that there is a parallel between the earthly high priest and a heavenly high priest who is the Angel of YHWH/kavod, but it predicts an eschatological fulfillment to priestly mediation. We are told in Numbers 25:13 that God has promised the Levites an eternal priesthood. Nevertheless, the priesthood still is under the Sinaitic covenant and its curses. If so, then the whole of the priesthood’s failure and sinfulness would logically disqualify them to possess a perpetual priesthood as it did with the house of Eli in 1 Samuel. To maintain the promise of eternal priesthood, God must act to purify creation and the make the priesthood function in a final eschatological act.
Such an implicit eschatological expectation becomes more explicit in the writings of the later prophets. In Malachi 3:3, we are told that God himself will come to purify the sons of Levi. The text also tells us that God himself will come to his Temple to purify it in the form of the Angel of the Lord: "Behold, I send my messenger [or "My Angel"], and he will prepare the way before me. And the Lord whom you seek will suddenly come to his temple; and the messenger of the covenant [or "Angel of the Covenant"] in whom you delight, behold, he is coming, says the LORD of hosts" (Mal 3:1, emphasis added). This connects with the expectation of the return of God to Zion, found in Isaiah 40 and Ezekiel 37-39. In Zechariah 3, we are told that the Angel of YHWH's purification of the high priest (v. 8) prefigures God's eschatological action of redemption: "I will remove the iniquity of this land in a single day"(v. 9).
The descriptions of the actions of the eschatological high priest are scattered throughout the Old Testament in a variety of interconnected texts. As we have already noted, the Servant of YHWH in the later chapters of Isaiah is identified as the new Passover lamb, necessitated by the new exodus. He is, as we have also suggested, identified in chapter 49 and 63 with the Angel of YHWH and the kavod. This identification is deepened by the description of the Angel of YHWH in Isaiah 63:9 as possessing both robes soaked in blood (Isa 63:2) and the role of the divine warrior (v. 1-5), much like Leviticus' portrayal of the high priest. As was previously noted, the Angel of YHWH is also said in v. 9 to be afflicted with the afflictions of the people in order to redeem them. Isaiah then harkens back to the time of the exodus and states that this same Angel (as is clear from the text of the Pentateuch as well) guided and redeemed Israel in the first exodus. He is described as being "his [God's] glorious arm"(v.12). This is identical with the description of the Servant in Isaiah 53:1 as "the arm of the LORD." This wording therefore further identifies the sufferings of the Angel of YHWH and the Servant, and thereby positively demonstrates them to be the same figure. In the same way also atonement leads to a universal Jubilee. We are told that the Servant announces such a Jubilee in Isaiah 61 and that he will justify many in chapter 53."