Fulgentius of Ruspe

In his own words on Deuteronomy

• Deuteronomy 6:4

  Therefore, in whatever place you may be, because you know that you have been baptized in the one name of the Father and the Son and the Holy Spirit, according to the rule promulgated by the command of our Savior, retain this rule with your whole heart, from the start and without hesitation: the Father is God, and the Son is God, and the Holy Spirit is God. This means the holy and ineffable Trinity is by nature one God, concerning whom it is said in Deuteronomy, "Hear, O Israel, the Lord your God is one God," and "You shall adore the Lord your God and him alone shall you serve." Indeed, … we have said that this one God who alone is true God by nature, is not the Father only, nor the Son only, nor the Holy Spirit only but is at one and the same time Father, Son and Holy Spirit. [Thus] we must be wary that while we say in truth that as the Father, Son, and Holy Spirit are one God, insofar as this is a unity of nature, we dare not say or believe something altogether blasphemous. [Such a blasphemous saying would be] that he who is the person of the Father is the same as either the Son or the Holy Spirit, or that he who is the person of the Son is the Father or the Holy Spirit. Or [it might be] that we dare to say or to believe that the person who is properly called the Holy Spirit in the confession of this Trinity is either the Father or the Son, something that is altogether wicked.

  TO PETER ON THE FAITH 1.3