28 And thus sins, because they are not forgiven out of the Church, must be forgiven by that Spirit, by whom the Church is gathered together into one. In fact, if any one out of the Church repent him of his sins, and for this so great sin whereby he is an alien from the Church of God, has an heart impenitent, what does that other repentance profit him? Seeing by this alone he speaks a word against the Holy Ghost, whereby he is alienated from the Church, which has received this gift, that in her remission of sins should be given in the Holy Ghost?
Which remission though it be the work of the Whole Trinity, is yet understood specially to belong to the Holy Spirit. For He is the Spirit of the adoption of sons, “in whom we cry Abba, Father;” that we may be able to say to Him, “Forgive us our debts.” And, “Hereby we know” as the Apostle John says, “that Christ dwells in us, by His Spirit which He has given us.” “The Spirit Itself bears witness with our spirit that we are the children of God.” For to Him appertains the fellowship, by which we are made the one body of the One only Son of God.
Whence it is written, “If there be therefore any consolation in Christ, if any comfort of love, if any fellowship of the Spirit.” With a view to this fellowship they to whom He first came spoke with the tongues of all nations. Because as by tongues the fellowship of mankind is more closely united; so it behooved that this fellowship of the sons of God and members of Christ which was to be among all nations should be signified by the tongues of all nations; that as at that time he was known to have received the Holy Ghost, who spoke with the tongues of all nations; so now he should acknowledge that he has received the Holy Ghost, who is held by the bond of the peace of the Church, which is spread throughout all nations.
Whence the Apostle says, “Endeavouring to keep the unity of the Spirit in the bond of peace.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)