Acts 2
The Procession of the Spirit — John 15:26
John 15:26 speaks of "the Spirit of truth, who proceeds from the Father." On this verse hangs the doctrine of procession and, eventually, the long filioque controversy between East and West. Augustine taught that the Spirit proceeds from the Father and the Son as the bond of love, a formula the West added to the Nicene Creed and the East rejected. Gregory of Nazianzus had insisted the Spirit's procession is as mysterious as the Son's generation. The Spirit's witnessing role connects to regeneration in John 3:6-8 and to Pentecost's promise in Acts 2:17. The same Spirit who proceeds is poured out on the church.
The Church as the Body of Christ — 1 Corinthians 12
1Cor 12:12-27: "for just as the body is one and has many members... so it is with Christ." By one Spirit all are baptized into one body, and the diversity of gifts serves the common good. Augustine's totus Christus — the whole Christ, head and members — expresses this unity, and Calvin treated the church as the mother of believers. The Catechism develops the body-of-Christ image for the communion of saints. The Spirit who distributes gifts here is the same Spirit of John 15:26 and Pentecost in Acts 2:17. The one baptism into one body connects to Rom 6:3 and Eph 4:4-6.
Pentecost and the Outpoured Spirit — Acts 2
Acts 2:16-21 interprets Pentecost as the fulfillment of Joel: "I will pour out my Spirit on all flesh." The ascended Christ sends the Spirit, and the last days begin with the birth of the church. Augustine preached Pentecost as the love of God poured into the church, the reversal of Babel, and Calvin treated the outpouring as the public inauguration of the Spirit's new-covenant ministry. The Spirit given here is the same who proceeds in John 15. Pentecost fulfills the promise of the Spirit in John 15:26 and the new heart of Ezek 36:27. It constitutes the one body of 1Cor 12:13 and looks ahead to the consummation of Rev 21:3.