From a letter by Fulgentius of Ruspe, bishop
Notice, at the conclusion of our prayer we never say, “through the Holy Spirit,” but rather, “through Jesus Christ, your Son, our Lord.” Through the mystery of the Incarnation, Jesus Christ became man, the mediator of God and man. He is a priest for ever according to the order of Melchisedech. By shedding his own blood he entered once and for all into the Holy Places. He did not enter a place made by human hands, a mere type of the true one; but, he entered heaven itself, where he is at God’s right hand interceding for us. Quite correctly, the Church continues to reflect this mystery in her prayer.
This mystery of Jesus Christ the high priest is reflected in the apostle Paul’s statement: Through him, then, let us always offer the sacrifice of praise to God, the fruit of lips that profess belief in his name. We were once enemies of the Father, but have been reconciled through the death of Christ. Through him then we offer our sacrifice of praise, our prayer to God. He became our offering to the Father, and through him our offering is now acceptable. It is for this reason that Peter the apostle urges us to be built up as living stones into a spiritual house, a holy priesthood to offer spiritual sacrifices pleasing to God through Jesus Christ. This then is the reason why we offer prayer to God our Father, but through Jesus Christ our Lord.
When we speak of Christ’s priesthood, what else do we mean than the incarnation? Through this mystery, the Son of God, though himself ever remaining God, became a priest. To him along with the Father, we offer our sacrifice. Yet, through him the sacrifice we now offer is holy, living and pleasing to God. Indeed, if Christ had not sacrificed himself for us, we could not offer any sacrifice. For it is in him that our human nature becomes a redemptive offering. When we offer our prayers through him, our priest, we confess that Christ truly possesses the flesh of our race. Clearly the Apostle refers to this when he says: Every high priest is taken from among men. He is appointed to act on behalf of these same men in their relationship to God; he is to offer gifts and sacrifices to God.
We do not, however, only say “your Son” when we conclude our prayer. We also say, “who lives and reigns with you in the unity of the Holy Spirit.” In this way we commemorate the natural unity of the Father, Son and Holy Spirit. It is clear, then, that the Christ who exercises a priestly role on our behalf is the same Christ who enjoys a natural unity and equality with the Father and the Holy Spirit.