Problem: John declared Christ to be eternal and equal with God (John 1:1; 8:58; 20:28). But here Paul seems to say that Christ was only a creature, the first one born (created) in the universe.
Solution: Paul clearly declares Christ to be God in this very letter by saying He “created all things” (1:16) and has “the fullness of the Godhead” (2:9). The reference to “firstborn” does not mean He is the firstborn in creation, but the firstborn over creation (v. 15), since “He is before all things” (v. 17). “Firstborn” in this context does not mean the first one to be born, but the heir of all, the Creator and owner of all things. As Creator of “all things,” He could not have been a created thing.
“And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all things he might have the preeminence.