In The Son of God, Martin Hengel notes (based on 1 Cor. 8:6) that "the Father is the primal ground and goal of creation, whereas Christ is the mediator" (13).
Next, Hengel discusses the Alexandrian philosopher Philo; according to Philo, the Platonic realm of transcendent Forms (Ideas) is God's 'eldest and firstborn son' and is synonymous with God's LOGOS (divine reason immanent in the cosmos). To Philo, the LOGOS is the "mediator between the eternal Godhead and the created, visible world." At the same time, the Logos is also God's "image" (EIKWN).
Philo is never quite clear about what he perceives the LOGOS to be. In varying delineations, he refers to the LOGOS as the sinless mediator, the spiritual primal man, the spokesman, the archangel, and the second god (deuteros theos). This deuteros theos is neither created nor uncreated, yet Philo does not equate the EIKWN of God with God himself (52). This claim is proved by referencing Somn. I, 157, 228-230.
In this portion of his famous work, Philo calls the EIKWN THEOU, both kurios and archangel. This point is significant because it is here that he distinguishes the LOGOS from the Father who brings forth the LOGOS. The Father is ho theos, but the LOGOS can only be considered theos (without the article). This datum substantiates the point that Philo viewed this agent as mediator of creation and a secondary god, possibly inferior to the Father of Israel (Isa. 64:8).
This philosophical detour alerts us to the fact that EIKWN when used by Philo does not mean that a thing is to be equated fully with its prototype. The sun's reflection in the water is not the same as the actual sun: it does not possess the same nature (essence or quidditas) that the sun does. Similarly, Jesus as the EIKWN of God, does not possess the substance of the Father, but is homoiousios with him. One day anointed Christians will enjoy this same privilege, to a lesser degree of course, when they experience glorified life in the EIKWN of the Son--being made like unto his image and that of his Father's.