The word prÅxtotokos ("firstborn"), while often used in the literal sense of the first to come from the womb, takes on a metaphorical significance based on the ancient attribution of preeminence to the first to be born. Thus, Israel is called God's "firstborn" (Exod. 4:22), and God says of David in Psalm 89:27 that "I will appoint him to be my firstborn, the most exalted of the kings of the earth." This latter text is probably especially important for Colossians 1:15, since Psalm 89 rings with messianic allusions, and Paul has just been describing Christ in messianic/kingly terms (vv. 12-14). It may be noted in this regard that the author to the Hebrews also uses prÅxtotokos as a christological title in a messianic context (Heb. 1:6; cf. v. 5)
Moo, D. J. (2008). The letters to the Colossians and to Philemon (p. 119). Grand Rapids, MI: William B. Eerdmans Pub. Co.