Then he opened their minds to understand the Scriptures, and said to them, “Thus it is written, that the Christ should suffer and on the third day rise from the dead, and that repentance and forgiveness of sins should be proclaimed in his name to all nations, beginning from Jerusalem. You are witnesses of these things. And behold, I am sending the promise of my Father upon you. But stay in the city until you are clothed with power from on high.” (Luke 24:45-49)
Making every composition teacher happy, at the conclusion of his first book Luke provides an excellent introduction to his second book. The Trinitarian conclusion of Luke is right were the book of Acts picks up.
Acts 1:4 and 2:33 make it clear that “the promise” Jesus speaks of is the sending of the Holy Spirit. Luke 24:49 has the same Trinitarian interconnectedness of Acts 2:33. Jesus sends the Spirit from the Father to his people.
It is the Holy Spirit, sent by the Son from the Father who clothes Christ’s disciples with power. The Spirit transforms cloistered cowards into a confessional community. Empowered by this promised gift of the Spirit (Is. 32:14-15; 44:3-4; 59:20-21; Joel 2:28-32; John 14:16-17); the disciples will powerfully preach the crucified and risen Christ receiving into their fellowship all who were appointed by the Father (Acts 13:46-52).
This concludes my survey of passages in Luke and Acts that refer to the Trinity. For those who have not been keeping score, in Luke-Acts there are references to the Trinity in: