>>571996
>All three are without cause
All three are God by nature and not by grace or by participation in the Father's essence.
However, the Father is nonetheless the cause of the Son's hypostasis by generation, and of the Holy Spirit's hypostasis by procession. There is one God because there is one Father. If the Father, the Son, and the Holy Spirit are all individually and self-sufficiently God, then they cannot be of one essence and nature.
>But that does not make them dependent on Him. The Son and the Holy Spirit are autotheos.
Strictly speaking, only the Father is autotheos, in that He is both God by nature and the source of all divinity.
The Son and the Holy Spirit are only autotheos insofar as they are God by nature, but, somewhat paradoxally, they have this nature from within the Father. The Father really is the source of all divinity, even in relation to the Son and to the Holy Spirit. That's His hypostatic quality.
>If it is licit to depict the preincarnate Christ just because He eventually became incarnate then there is no command against depicting God at all.
The Father, the Son, and the Holy Spirit appeared physically to Abraham. Not a true case of incarnation, but regardless, they really did appear physically in some form to him, and so we can depict them in the form they have revealed themselves.
The Father has only revealed Himself in these ways: Abraham saw Him as an angel, Moses saw His "back" and His "hand," and that's about it. As a result, canonically, He can only be depicted as a hand (also how Jews depicted Him before they went full iconoclast in reaction to the Christians) or as an angel in Rublev's icon.
The Son has revealed Himself in these ways: Abraham saw Him as an angel (and He appeared several more times as an angel in the OT), David saw Him as the Ancient of Days, He was of course incarnate as a man of flesh and bones, He also appeared to the apostles in His resurrected and transfigured body (a reality He let Peter, John, and James see some time before His death too). So that is what we can depict Him as.
The Holy Spirit has revealed Himself in these ways: as an angel to Abraham, as a dove when Jesus was baptized in the Jordan, as tongues of fire at Pentecost. So that is what we can depict Him as.
But note that these depictions are also contextual - for instance, the Father appeared as an angel to Abraham, but only in this context, so we can only depict Him that way when it is in that context. Similarly, the Holy Spirit appeared as a dove at the baptism in the Jordan, but only in this context, so we can only depict Him that way when it is in that context. There's a bit more liberty with the Son since He did not appear as if in a prophetic vision, but rather He truly became a man.