Does Colossian 2:9 mean that Jesus is the Father, Son, and Holy Spirit?
"For in Him all the fullness of Deity dwells in bodily form" (Colossians 2:9).
"Fullness" (from the Greek word pleroma) means a complete or full expression. Thus, in Galatians 4:4 the fullness of time doesn't mean all time but the moment in time that was the perfect time for Christ to die. Or in "For I do not want you, brethren, to be uninformed of this mystery -- so that you will not be wise in your own estimation--that a partial hardening has happened to Israel until the fullness of the Gentiles has come in" (Romans 11:25). Again, this is not saying all the Gentiles, but when a great mass of Gentiles are converted to Christianity.
In Colossians 1:19 and Colossians 2:9 it is saying that Christ completely represented every attribute of the Godhead while being in human form. "And the Word became flesh, and dwelt among us, and we saw His glory, glory as of the only begotten from the Father, full of grace and truth" (John 1:14). As Albert Barnes once wrote, "We have a Saviour who is in no respect deficient in wisdom, power, and grace to redeem and save us."
In the same way, the church is to be a complete representation of who Christ is. "And He put all things in subjection under His feet, and gave Him as head over all things to the church, which is His body, the fullness of Him who fills all in all" (Ephesians 2:22-23). See also Ephesians 3:19.