God not The Father
There are three reasons why God as it is used here should not be understood as The Father.
- God as used in the OT
- God and Father as used in the NT
- God and Father as used in this letter
The Old Testament makes no mention of God the Father in the sense it is used in the New. Therefore, passages drawing upon the Old Testament (see below), should not qualify God using the new expressions. For example, Paul uses three phrases to specifically identify God as Father. Most common is θεοῦ πατρὸς ἡμῶν, God our Father. Less common is θεοῦ πατρὸς, God-Father, and on a few occasions he employs Sharp's Rule saying, ὁ θεὸς καὶ πατὴρ, the God and Father. None of these terms are used in the LXX. They are New Testament terminology employed to make specific reference to the Father. Therefore, having developed new phrases for the sole purpose of making specific reference to the Father, one must conclude the failure to use the new terminology indicates Father is not intended.
The new terminology is used elsewhere in Colossians:
To the saints and faithful brothers in Christ at Colossae; Grace to you and peace from God our Father. (Colossians 1:2 ESV)
And whatever you do, in word or deed, do everything in the name of the Lord Jesus, giving thanks to God the Father through him. (Colossians 3:17)
In addition, the New Testament practice of distinguishing between God and God as Father, or simply Father, is also evident in the passage in question:
9 And so, from the day we heard, we have not ceased to pray for you, asking that you may be filled with the knowledge of his will in all spiritual wisdom and understanding, 10 so as to walk in a manner worthy of the Lord, fully pleasing to him: bearing fruit in every good work and increasing in the knowledge of God; 11 being strengthened with all power, according to his glorious might, for all endurance and patience with joy; 12 giving thanks to the Father, who has qualified you to share in the inheritance of the saints in light. 13 He has delivered us from the domain of darkness and transferred us to the kingdom of his beloved Son, 14 in whom we have redemption, the forgiveness of sins. 15 He is the image of the invisible God, the firstborn of all creation. (Colossians 1)
Therefore, a proper exegesis of image of God, ὅς ἐστιν εἰκὼν τοῦ θεοῦ, should recognize Paul's terminology, τοῦ θεοῦ (the God) cannot be understood as a specific identification of the Father.
image of God - εἰκὼν τοῦ θεοῦ
In other letters, Paul compares Jesus to the first man:
Thus it is written, “The first man Adam became a living being”; the last Adam became a life-giving spirit. (1 Corinthians 15:45)
12 Therefore, just as sin came into the world through one man, and death through sin, and so death spread to all men because all sinned— 13 for sin indeed was in the world before the law was given, but sin is not counted where there is no law. 14 Yet death reigned from Adam to Moses, even over those whose sinning was not like the transgression of Adam, who was a type of the one who was to come. 15 But the free gift is not like the trespass. For if many died through one man's trespass, much more have the grace of God and the free gift by the grace of that one man Jesus Christ abounded for many. 16 And the free gift is not like the result of that one man's sin. For the judgment following one trespass brought condemnation, but the free gift following many trespasses brought justification. 17 For if, because of one man's trespass, death reigned through that one man, much more will those who receive the abundance of grace and the free gift of righteousness reign in life through the one man Jesus Christ. (Romans 5)
The expression image of God was used to describe the first man:
And God made man, according to the image of God he made him, male and female he made them. (LXX-Genesis 1:27)
καὶ ἐποίησεν ὁ θεὸς τὸν ἄνθρωπον κατ᾽ εἰκόνα θεοῦ ἐποίησεν αὐτόν ἄρσεν καὶ θῆλυ ἐποίησεν αὐτούς
In Colossians, by employing the phrase image of God, Paul has made another Adam/Jesus comparison. The first man was made according to the image of God. But Jesus is the image of God. Furthermore, by using the general expression of God, Paul eliminates understanding image of the Father, which could be seen as contradicting the equality between Jesus and the Father as stated in the Fourth Gospel. That is, image of God is in harmony with equality with the Father, but image of the Father would imply inequality.
As with his other statements equating Jesus and God, Paul does not "fill in the blank." He does not enumerate the qualities. This lack of specificity is no different than the Hebrew term Elohim. No explanation is given to explain why the singular God is most often identified using the plural Elohim. In a sense, it must simply be accepted as stated. Nevertheless, a lack of "full disclosure" is hardly reason to reject the literal meaning of the text. Paul and other New Testament writers all agree on the most significant God-like quality. Jesus was without sin; He is holy.
Finally, in making this comparison to Adam, Paul had the ideal opportunity to make a more precise comparison to Adam by saying Jesus was made. Yet, not only does Paul avoid language which could imply Jesus was a created being, he makes the point Jesus is. Then he immediately follows with a list of actions the Old Testament states are reserved for God.
For by him all things were created, in heaven and on earth, visible and invisible, whether thrones or dominions or rulers or authorities—all things were created through him and for him. (Colossians 1:16)
My Trinitarian Conclusion
First, the expression in the context of the letter demonstrates God is no longer an adequate term to describe divine interaction with mankind. Unlike the Old Testament, theos is not self-explanatory. New Testament writers are compelled to distinguish between God, and God the Father. This change in terminology is exactly what I would expect if those educated under the Old Testament understood the more complete revelation of God as found in the New Testament. In other words, from the Old Testament vorlage, God the Father only makes sense from a Trinitarian understanding of God. Otherwise the New Testament burdens the reader with unnecessary terminology.
Second, by stating Jesus is the image of God, Paul distinguishes between the pre-existent uncreated Son and Adam who was created according to the image of God.
Third, by following image of God with a list of divine actions, Paul reinforces the pre-existent uncreated status of the Son. Moreover, he implies the Son was active in making the first man according to the image of God.
Finally, in addition to other New Testament passages which describe Jesus using God-like terms such as glory or radiance, considering image of God in light of equality with the Father, leads me to conclude Colossians could also be understood as He, the Father, is also the image of God.