Psalm 89 is in today’s Psalm readings (29,59,89,149). I feel compelled to point something out every time we come to this Psalm, since the idea of “firstborn” is perverted by those who deny Christ is the eternal Son of God.
“I have said, ‘Lovingkindness will be built up forever; in the heavens You will establish Your faithfulness. I have made a covenant with My chosen; I have sworn to David My servant, I will establish your seed forever and build up your throne to all generations’...He will cry to Me, 'You are my Father, My God, and the rock of my salvation.’ I also shall make him My firstborn, the highest of the kings of the earth. My lovingkindness I will keep for him forever, and My covenant shall be confirmed to him. So I will establish his descendants [“seed,” singular as in vs. 4] forever and his throne as the days of heaven” (Psalm 89:2-4,26-29).
Jesus Christ, “seed of David according to the flesh” (Romans 1:3), Who has “the throne of His father David...and [Whose] kingdom will have no end” (Luke 1:32,33), is the eternal Son of God. He is the “firstborn” (Romans 8:29; Colossians 1:15,18; Hebrews 1:6; Revelation 1:5). What does this mean for the eternal Son of God? Learn from Psalm 89:27 that the Bible’s definition of “firstborn” does not mean “created” or “did not exist before being begotten.” It is the language of enthronement: in the Father’s covenant with His Son, to be declared “firstborn” is to be proclaimed “highest of the kings of the earth.” Do not be led astray by those who rely on their own understanding to lower Christ by their own definition of “firstborn.”
The eternal Son of God, the Person of the Son in the Godhead Who has "neither beginning of days nor end of life" (Hebrews 7:3), is also the King of kings and Lord of lords according to the unchanging and unalterable promise of His Father. He rules and reigns, so obey and teach others to obey this timeless Sovereign!
“And Jesus came up and spoke to them, saying, ‘All authority has been given to Me in heaven and on earth. Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit, teaching them to observe all that I commanded you; and lo, I am with you always, even to the end of the age’” (Matthew 28:18-20).