Colossians 1:15 He is the image of the invisible God, the firstborn over all creation.

The Son of God, the Second Person of the Trinity, is eternal in his being (John 1:1; 8:58, 20:28, etc.). Paul also agrees with this saying, "For by him all things were created: things in heaven and on earth, visible and invisible, whether thrones or powers or rulers or authorities; all things were created by him and for him" (Col. 1:16). So, since Paul is not disagreeing with himself what does he mean by the expression, "the firstborn over all creation?"

Our text is not saying Christ is the firstborn in all creation, but the firstborn over all creation. He is the creator and heir of all things. In the Old Testament, a firstborn son would be the primary heir of an estate (Deut. 21:17; Ex. 4:22; Ps. 89:27). Christ is accorded a similar honor and dignity. Christ is loved by his Father (Col. 1:13), and all things were created in him, by him, and for him (Col. 1:16-17), so he is the rightful heir.

Jesus' resurrection marks the beginning of a new creation (2 Cor. 5:17; cf. Col. 3:10). As the first to rise from the dead, Christ inaugurated the new age anticipated in the Old Testament (Acts 2:29-36; 13:32-35) and founds a new humanity in himself to replace the old humanity in Adam (1 Cor. 15:45, 47). His own resurrection is an anticipation and a guarantee of the resurrection that all believers will one day enjoy (Rom. 8:29; 1 Cor. 15:2028; Heb. 1:6; 12:23). Without detracting from the glory the pre-existent Son already had with the Father, the New Testament teaches that Christ's resurrection marks out for him a new and higher standing, and wins for him an even greater name (Acts 13:33, 34; Rom. 1:4; Eph. 1:20-23; Phil. 2:1-11; Heb. 1:4-5). By virtue of his resurrection from the dead, Jesus Christ is Lord of the universe that was created by him, that he has always sustained, in which he redeemed the elect, and in which all things will be reconciled to him in the new heavens and the new earth.

Reference

Pratt, Richard, gen. ed. Spirit of the Reformation Study Bible. Grand Rapids, MI: Zondervan, 2003.