The Angel of Jehovah is God Himself in His Divine Trinity serving His elect as a Servant (cf. Heb. 1:14). The embodiment of the Triune God is Christ, and Christ is the Angel of Jehovah, who took care of Israel as Jehovah in action in the Old Testament (see note Exo. 3:21b). For Christ to be the Angel of Jehovah means that God has appointed and commissioned Himself in His Divine Trinity to act in caring for His people.
Because Israel did not act as a proper wife, the very Jehovah who was the Husband, the Head, and the King of Israel became a Servant to His wife. He came to her not as a Husband, Head, or King but as the Angel of Jehovah, who was sent by Jehovah (Zech. 2:9-11). Since Israel did not regard Jehovah as the Head, He became a Servant to serve her. His word to Israel in vv. 1-3 was not a rebuke or a command but the admonition of a servant.