Epiphanius Ancoratus 10

For there is nothing that can be confirmed without the testimonies of two or three witnesses.  It was to this kind of figure that a certain mystery was confirmed. For those who lived under the Law merely acknowledged the Father, but were not quite ready to receive the power of the Son. But through the two of them their testimonies might be strengthened. Then with the testimony of the third, the Holy Spirit, they may hold fast to it and join in with the chorus of the Seraphim and Cherubim crying Holy, Holy, Holy. It is not just the sound of two voices that the divine glory in heaven is proclaimed. Neither is there a fourth holy thing to be seen nor is there any spiritual creature that claim some fourth thing or one thing. There are three expressions in which we cry, Holy, Holy, Holy! They don’t say Holies, Holies as to attribute something that has many names so as to try and disguise the three. But we declare three times in one specific way a specific kind of holiness that rules out anything that remotely appears polytheistic.  Therefore, the Holy takes rest among the Holy Ones, for the true Father mutually indwells the Son and the Holy Spirit, the Son mutually indwells the Father and the Holy Spirit, and the Holy Spirit mutually indwells the Father and the Son, they are three in number, one in divinity, of one Being, of one glory: one God. When we say one God the only one that comes to mind is the Trinity. You have taken hold of the Holy Spirit therefore you have laid hold of the power of the Father and the Son of God. You have declared publicly the Father and by declaring Him you signify the Son and the Holy Spirit in unity with Him. The Father is the Father, the Son is the Son and the Holy Spirit is the Holy Spirit. The Trinity cannot alienate itself from its unity and identity. The Father is honoured insofar that He is Father; the Son is honoured insofar that He is the Son; and finally the Holy Spirit is honoured insofar as He is truly the Spirit of God. And this is what the Only-Begotten asserts: Whoever honours the Father, honours the Son (Jn. 5.23). When you call the Father, “Father,” you indicate and honour the Son, and when you honour the Son you honour the Father. For when you call the Son, “Son,” you honour the Father showing that you do not disrespect Christ by making Him inferior to the Father.