"[Psalm 110:1] The Lord says. For the name the Lord, also in vv. 2 and 4, see Ex 6:3 note. What the Lord says is expressed in the original by the noun "oracle," i.e., a divine communication or revelation which the prophets transmit to their hearers with the introduction: "Thus says the Lord." (2 Ch 34:26)
My Lord. The Hebrew noun denotes a respected or superior person. It is used as a title in addressing kings and other dignitaries (Gn 19:2; 23:6; 1 Sm 22:12; 2 Sm 13:32). The king to or "concerning" whom this prophetic oracle speaks is by that very word of God made to be the "King of kings and Lord of lords" (Rv 19:16). His elevation to the right hand of power is to coincide with the defeat of enemies, reduced to serve as a footstool (Jos 10:24; 1 K 5:3). For the fulfillment of this promise see Acts 2:25; 1 Co 15:25; Heb 1:13; 10:13."
Martin Franzmann, Concordia Self-study Commentary [commentary on Psalms], p. 395-396
My Lord. The Hebrew noun denotes a respected or superior person. It is used as a title in addressing kings and other dignitaries (Gn 19:2; 23:6; 1 Sm 22:12; 2 Sm 13:32). The king to or "concerning" whom this prophetic oracle speaks is by that very word of God made to be the "King of kings and Lord of lords" (Rv 19:16). His elevation to the right hand of power is to coincide with the defeat of enemies, reduced to serve as a footstool (Jos 10:24; 1 K 5:3). For the fulfillment of this promise see Acts 2:25; 1 Co 15:25; Heb 1:13; 10:13."
Martin Franzmann, Concordia Self-study Commentary [commentary on Psalms], p. 395-396