outpouring of the Holy Spirit
Acts 1:5, 8
5 "for John truly baptized with water, but you shall be baptized with the Holy Spirit not many days from now." . . . . 8 "But you shall receive power when the Holy Spirit has come upon you; and you shall be witnesses to Me in Jerusalem, and in all Judea and Samaria, and to the end of the earth."
1 Thess 1:5
For our gospel did not come to you in word only, but also in power, and in the Holy Spirit and in much assurance, as you know what kind of men we were among you for your sake.
1 Peter 1:10-12
10 Of this salvation the prophets have inquired and searched carefully, who prophesied of the grace that would come to you,11 searching what, or what manner of time, the Spirit of Christ who was in them was indicating when He testified beforehand the sufferings of Christ and the glories that would follow. 12 To them it was revealed that, not to themselves, but to us they were ministering the things which now have been reported to you through those who have preached the gospel to you by the Holy Spirit sent from heaven--things which angels desire to look into.
See also: Justification by Faith and the Work of the Holy Spirit