The Holy Spirit is the third person of the Trinity: God with the Father and the Son, the Lord and giver of life. The Church’s teaching on where he comes from, from the Father and the Son as from one principle, is set out in the Creed, the councils and the catechisms.
Before his Passover, Jesus announced the sending of "another Paraclete" (Advocate), the Holy Spirit. At work since creation, having previously "spoken through the prophets", the Spirit will now be with and in the disciples, to teach them and guide them "into all the truth". The Holy Spirit is thus revealed as another divine person with Jesus and the Father.
The eternal origin of the Holy Spirit is revealed in his mission in time. The Spirit is sent to the apostles and to the Church both by the Father in the name of the Son, and by the Son in person, once he had returned to the Father. The sending of the person of the Spirit after Jesus' glorification reveals in its fullness the mystery of the Holy Trinity.
The apostolic faith concerning the Spirit was confessed by the second ecumenical council at Constantinople (381): "We believe in the Holy Spirit, the Lord and giver of life, who proceeds from the Father." By this confession, the Church recognizes the Father as "the source and origin of the whole divinity".
But the eternal origin of the Spirit is not unconnected with the Son's origin: "The Holy Spirit, the third person of the Trinity, is God, one and equal with the Father and the Son, of the same substance and also of the same nature... Yet he is not called the Spirit of the Father alone,... but the Spirit of both the Father and the Son." The Creed of the Church from the Council of Constantinople confesses: "With the Father and the Son, he is worshipped and glorified."
The Latin tradition of the Creed confesses that the Spirit "proceeds from the Father and the Son (filioque)". The Council of Florence in 1438 explains: "The Holy Spirit is eternally from Father and Son; He has his nature and subsistence at once (simul) from the Father and the Son. He proceeds eternally from both as from one principle and through one spiration.... And, since the Father has through generation given to the only-begotten Son everything that belongs to the Father, except being Father, the Son has also eternally from the Father, from whom he is eternally born, that the Holy Spirit proceeds from the Son."
Who is the Paraclete that Christ promises, from whom does he proceed, and by whom is he sent?
In the Epistle to the Galatians Paul says that God hath sent the Spirit of his Son into our hearts. The Spirit is sent by the Father and is named the Spirit of the Son. It bears on the doctrine that the Holy Ghost is sent by the Father and the Son, and that his mission manifests his eternal procession.
And because you are sons, God hath sent the Spirit of his Son into your hearts, crying: Abba, Father.
In the Epistle to the Romans Paul speaks of the Spirit of God and the Spirit of Christ in the same passage, as dwelling in the faithful. The Latin writers read the double name as pointing to the Spirit’s relation to the Son. It bears on the doctrine that the Holy Ghost is the Spirit of Christ and is sent by him.
But you are not in the flesh, but in the spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.
In the Acts of the Apostles Peter tells Ananias that in lying to the Holy Ghost he has lied to God. The one rebuke passes from the Holy Ghost to God without a break. It bears on the doctrine that the Holy Ghost is truly God.
But Peter said: Ananias, why hath Satan tempted thy heart, that thou shouldst lie to the Holy Ghost and by fraud keep part of the price of the land? Whilst it remained, did it not remain to thee? And after it was sold, was it not in thy power? Why hast thou conceived this thing in thy heart? Thou hast not lied to men, but to God.
In the farewell discourse of the Gospel according to John, Jesus promises another Paraclete, the Spirit of truth, who will abide with the disciples for ever, and says the Father will send him in the Lord’s name. He is the one who teaches and brings to mind. It bears on the doctrine that the Holy Ghost is a divine person, sent by the Father in the name of the Son.
And I will ask the Father: and he shall give you another Paraclete, that he may abide with you for ever: The spirit of truth, whom the world cannot receive, because it seeth him not, nor knoweth him. But you shall know him; because he shall abide with you and shall be in you.
But the Paraclete, the Holy Ghost, whom the Father will send in my name, he will teach you all things and bring all things to your mind, whatsoever I shall have said to you.
In the Gospel according to John the Lord speaks of the Paraclete whom he will send from the Father, the Spirit of truth who proceedeth from the Father. The Eastern tradition rests its confession of the Spirit’s origin on these words, and the Latin tradition holds them together with the sending by the Son. It bears on the Father as source and on the Son’s part in the mission.
But when the Paraclete cometh, whom I will send you from the Father, the Spirit of truth, who proceedeth from the Father, he shall give testimony of me.
In the Gospel according to John the Lord says the Spirit of truth shall receive of what is his, and that all things the Father hath are his. The Fathers read these words as pointing to the Spirit’s relation to the Son. It bears on the doctrine that the Holy Ghost proceeds from the Father and the Son.
But when he, the Spirit of truth, is come, he will teach you all truth. For he shall not speak of himself: but what things soever he shall hear, he shall speak. And the things that are to come, he shall shew you. He shall glorify me: because he shall receive of mine and shall shew it to you. All things whatsoever the Father hath are mine. Therefore I said that he shall receive of me and shew it to you.