I do not see any clear references to the Trinity in Acts 3 by itself. Nevertheless, there is something that is foundational to an orthodox understanding of the Trinity.
And now, brothers, I know that you acted in ignorance, as did also your rulers. But what God foretold by the mouth of all the prophets, that his Christ would suffer, he thus fulfilled. Repent therefore, and turn again, that your sins may be blotted out, that times of refreshing may come from the presence of the Lord, and that he may send the Christ appointed for you, Jesus, whom heaven must receive until the time for restoring all the things about which God spoke by the mouth of his holy prophets long ago.
This first half of this chapter recounts the healing of the lame beggar at the gate of the temple. The second half of the chapter is Peter’s address to the astonished crowd. Verses 18 and 21 repeat the same idea with slightly differing terminology: the Old Testament prophets were speaking the words of God. Given the hundreds of times the phrase “the word of the Lord” appears in the Old Testament this is certainly no paradigm altering statement by Peter. It is unlikely faithful Jews would take issue with Peter’s assertion. But consider Peter’s words in each of his epistles:
Concerning this salvation, the prophets who prophesied about the grace that was to be yours searched and inquired carefully, inquiring what person or time the Spirit of Christ in them was indicating when he predicted the sufferings of Christ and the subsequent glories.
1 Peter 1:10-11
For no prophecy was ever produced by the will of man, but men spoke from God as they were carried along by the Holy Spirit.
2 Peter 1:21
Acts 3 is an important text for Trinitarian studies because it teaches that the Holy Spirit is called God by the New Testament authors. In Acts 3, God moved and spoke through the prophets. In 1 & 2 Peter, the Holy Spirit moved and spoke through the prophets. Did Peter really think this way? Would he specifically call the Holy Spirit God? After all, the events of Acts and the writings of his epistles are separated by thirty years. Yet I do not think this was just a slip of the tongue. For in Acts 5 Peter calls refers to the Holy Spirit as God within the space of 30 seconds—not years (cf. Acts 5:3-4).
Bringing in Peter’s epistles as a cross reference to Acts 3 demonstrates that the apostle considered the Holy Spirit God. The three references also form more support for the co-operation of the Trinity. How exactly did the Old Testament prophets receive their message?
- God foretold (Acts 3:18)
- God spoke (Acts 3:21)
- Spirit of Christ . . . predicted (1 Peter 1:11)
- Spoke from God . . . by the Holy Spirit (2 Peter 1:21)
The denial of Scripture is a denial of the Trinity. The denial of the Trinity is a denial of Scripture.