Who do you bow to? Who truly holds the highest authority in your life? The Psalmist declares God not just as 'a' king, but 'my King'.
David doesn't just acknowledge God as a supreme ruler, but as his personal King. This isn't a distant, theoretical authority, but a relationship. He is "my God, O King." This title speaks of God's supreme, undeniable sovereignty over all creation, but also invites a personal allegiance. He is the King of kings, the one to whom all earthly rulers owe their authority and to whom we all owe our obedience. To call Him 'my King' means recognizing His right to rule not just the cosmos, but my own life, my decisions, my desires.