O Christ our God, You ascended in Glory and gladdened Your disciples by the promise of the Holy Spirit. Your blessing assured them that You are the Son of God, the Redeemer of the world. Kontakion ...

And she conceived of the Holy Spirit. Hail Mary full of grace ... That we may be made worthy of the promises of Christ. Hail Mary... Let us pray, Pour forth, we beseech thee, O Lord, thy grace ...

Jesus had already promised these “mighty” works of the Paraclete: just reread what he said at the Last Supper, as recounted by John (15:26-16:15). The Holy Spirit does “mighty” things.