The Self-Donation of God, pg. 29:
"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)."