Jesus asked why King David called his son (meaning his descendant) his Lord. The implied answer was that the Christ was more than a human king from David's family line. He is Lord of all (see 2:11; Acts 10:36).
Psalm 110:1 became an important passage for the apostles. It confirms that Jesus is the Son of God (see Mark 14:62; Acts 2:34; 7:56; Romans 8:34; 1 Corinthians 15:25; Ephesians 1:20; Colossians 3:1; Hebrews 1:3, 13; 8:1; 10:12–13; 1 Peter 3:22; Revelation 3:21).