The peace and grace of the Father, the Son, and the Holy Spirit are one, so also is Their charity one, which showed itself chiefly in the redemption of man. Their communion with man is also one.
126. Therefore since the calling is one, the grace is also one. Lastly, it is written: “Grace unto you and peace from God our Father, and from the Lord Jesus Christ.” You see, then, that we are told that the grace of the Father and the Son is one, and the peace of the Father and the Son is one, but this grace and peace is the fruit of the Spirit, as the Apostle taught us himself, saying: “But the fruit of the Spirit is love, joy, peace, patience.” And peace is good and necessary that no one be troubled with doubtful disputations, nor be shaken by the storm of bodily passions, but that his affections may remain quietly disposed as to the worship of God, with simplicity of faith and tranquillity of mind.
127. As to peace we have proved the point; but as to grace the prophet Zechariah says, that God promised to pour upon Jerusalem the spirit of grace and mercy, and the Apostle Peter says: “Repent and be baptized every one of you in the Name of the Lord Jesus Christ for the remission of sins, and you shall receive the grace of the Holy Spirit.” So grace comes also of the Holy Spirit as of the Father and the Son. For how can there be grace without the Spirit, since all divine grace is in the Spirit?
128. Nor do we read only of the peace and grace of the Father, the Son, and the Holy Spirit, but also, faithful Emperor, of the love and communion. For of love it has been said: “The grace of our Lord Jesus Christ, and the love of God.” We have heard of the love of the Father. The same love which is the Father's is also the Son's. For He Himself said: “He that loves Me shall be loved of My Father, and I will love him.” And what is the love of the Son, but that He offered Himself for us, and redeemed us with His own blood. But the same love is in the Father, for it is written: “God so loved the world, that He gave His Only-begotten Son.”
129. So, then, the Father gave the Son, and the Son gave Himself. Love is preserved and due affection is not wronged, for affection is not wronged where there is no distress in the giving up. He gave one Who was willing, He gave One Who offered Himself, the Father did not give the Son to punishment but to grace. If you enquire into the merit of the deed, enquire into the description of the affection. The vessel of election shows plainly the unity of this divine love, because both the Father gave the Son and the Son gave Himself. The Father gave, Who “spared not His own Son, but gave Him up for us all.” And of the Son he also says: “Who gave Himself for me.” “Gave Himself,” he says. If it be of grace, what do I find fault with. If it be that He suffered wrong, I owe the more.
130. But learn that in like manner as the Father gave the Son, and the Son gave Himself, so, too, the Holy Spirit gave Him. For it is written: “Then was Jesus led by the Spirit into the wilderness to be tempted by the devil.” So, too, the loving Spirit gave the Son of God. For as the love of the Father and the Son is one, so, too, we have shown that this love of God is shed abroad by the Holy Spirit, and is the fruit of the Holy Spirit, because “the fruit of the Spirit is love, joy, peace, patience.”
131. And that there is communion between the Father and the Son is plain, for it is written: “And our communion is with the Father and with His Son Jesus Christ.” And in another place: “The communion of the Holy Spirit be with you all.” If, then, the peace of the Father, the Son, and the Holy Spirit is one, the grace one, the love one, and the communion one, the working is certainly one, and where the working is one, certainly the power cannot be divided nor the substance separated. For, if so, how could the grace of the same working agree?
Source: On the Holy Spirit (New Advent)