What does Psalm 110:4 mean?
This passage uses two terms with similar English translations. One is Yahweh, or YHWH, a term used exclusively for God (Exodus 3:15) and usually printed in small capitals as "Lord." The other is Adonai, a more general term which often applies to God and is printed with normal font as "Lord." Here, God the Father, Yahweh, continues to speak to the Son, Adonai (Psalm 110:1–3). This psalm speaks about the Messiah, a role fulfilled by Jesus Christ.Melchizedek is a mysterious figure who appeared to Abram (Genesis 17:5) after the defeat of Chedorlaomer's confederacy. He brought bread and wine and blessed Abram (Genesis 14:17–20). This figure is referred to as both king and priest (Genesis 14:18). Under the old covenant, only those of Levi could be priests, and only those of Judah could be kings. Yet Adonai—the "Lord"—was given kingly status (Psalm 110:2–3) and here is labelled a priest like Melchizedek.
The book of Hebrews explains how this points again to Jesus Christ as the fulfillment of God's prophecies (Hebrews 5:6, 10; 6:20). Chapter 7 goes into detail about what this means (Hebrews 7:17, 21). Hebrews chapter 8 applies this to explain that only Christ can be the Messiah, as only He is appointed both king and priest by God (Hebrews 8:1–2).