Jamieson, Fausset and Brown on Ezekiel 34:23

23. set up--that is, raise up by divine appointment; alluding to the declaration of God to David, "I will set up thy seed after thee" (2Sa 7:12); and, "Yet have I set My king on My holy hill of Zion" (Psa 2:6; compare Ac 2:30; 13:23).

one shepherd--literally, "a Shepherd, one": singularly and pre-eminently one: the only one of His kind, to whom none is comparable (So 5:10). The Lord Jesus refers to this prophecy (Joh 10:14), "I am THE Good Shepherd." Also "one" as uniting in one the heretofore divided kingdoms of Israel and Judah, and also "gathering together in one all things in Christ, both which are in heaven and on earth" (Ep 1:10); thus healing worse breaches than that between Israel and Judah (Col 1:20). "God by Him reconciling all things unto Himself, whether things in earth or in heaven."

David--the antitypical David, Messiah, of the seed of David, which no other king after the captivity was: who was fully, what David was only in a degree, "the man after God's own heart." Also, David means beloved: Messiah was truly God's beloved Son (Is 42:1; Mt 3:17). Shepherd means King, rather than religious instructor; in this pre-eminently He was the true David, who was the Shepherd King (Lu 1:32, 33). Messiah is called "David" in Is 55:3, 4; Jr 30:9; Ho 3:5.