How can the eternal Son of God be “the firstborn over all creation”?

In his letter to the Colossians, Paul calls Jesus Christ the “firstborn over all creation” (Colossians 1:15). How can Christ be both the eternal Creator of all things and yet himself be the firstborn? First, in referring to Christ as the firstborn, Paul has in mind preeminence. This usage is firmly established in the Old Testament. For example, Ephraim is referred to as the Lord’s “firstborn” (Jeremiah 31:9) even though Manasseh was born first (Genesis 41:51). Likewise, David is appointed the Lord’s “firstborn, the most exalted of the kings of the earth” (Psalm 89:27), despite being the youngest of Jesse’s sons (1 Samuel 16:10–13). While neither Ephraim nor David was the first one born in his family, both were firstborn in the sense of preeminence or “prime position.”

Furthermore, Paul refers to Jesus as the firstborn over all creation not the firstborn in creation. As such, “He is before all things and in him all things hold together” (Colossians 1:17, emphasis added). The force of Paul’s language is such that the cult of the Jehovah’s Witnesses, who ascribe to the ancient Arian heresy that the Son is not preexistent and coeternal with the Father, have been forced to insert the word “other” (e.g., “all other things”) in their deeply flawed New World Translation of the Bible in order to demote Christ to the status of a created being.

Finally, as the panoply of Scripture makes plain, Jesus is the eternal Creator who spoke and the limitless galaxies leapt into existence. In John 1 he is overtly called “God” (v. 1), and in Hebrews 1 he is said to be the one who “laid the foundations of the earth” (v. 10). And in the very last chapter of the Bible, Christ refers to himself as “the Alpha and the Omega, the First and the Last, the Beginning and the End” (Revelation 22:13). Indeed, the whole of Scripture precludes the possibility that Christ could be anything other than the preexistent sovereign of the universe.

http://www.equip.org/bible_answers/how-can-the-eternal-son-of-god-be-the-firstborn-over-all-creation-2/

Jesus, The firstborn over all creation.