Peter only has one reference to the Trinity in his second epistle, but what he lacks is quantity is more than made for in quality.
For we did not follow cleverly devised myths when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty. For when he received honor and glory from God the Father, and the voice was borne to him by the Majestic Glory, “This is my beloved Son, with whom I am well pleased,” we ourselves heard this very voice borne from heaven, for we were with him on the holy mountain. And we have something more sure, the prophetic word, to which you will do well to pay attention as to a lamp shining in a dark place, until the day dawns and the morning star rises in your hearts, knowing this first of all, that no prophecy of Scripture comes from someone’s own interpretation. 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 1:16-21)
Commentators are divided on multiple points in this brief passage. Is “the coming of our Lord Jesus Christ” a reference to the Christ’s first appearance (incarnation and ministry) or his second appearance (return and reign)? What is more sure—the witness of what the apostles saw (NIV; NKJV; NLT; NASB) or the record of the Old Testament prophets (KJV; ESV)? Is it the origin or the interpretation of Scripture that Peter has in mind in verse 20? Yet in all their wrangling over these issues, I have not read a single commentator bring out the Trinity in this passage.
The ESV—more than any other translation—comes tantalizingly close to bringing out the connection. In verses 17 and 18 Peter speaks of a voice “borne” from heaven to earth at the Transfiguration of Jesus. This voice was of course that of the Father once again declaring his approval of his Son. Other translations simply use some form of “come” or simply leave it out (NLT in verse 18). But Peter did not use one of the common New Testament words for come (paraginomai or erchomai). Peter used the term phero. I believe he did so very intentionally and I believe he did so to highlight the work of the Trinity in revelation.
The use of “borne” in verses 17 is significant because it is unusual. Peter could have simply used a verb indicating speech—“God said.” The use of “borne” in verse 18 is significant because it is unnecessary: as some translations do, Peter could have left out the phrase entirely. But instead Peter twice uses the common term phero—the generic term meaning to bring, carry, move, bear something.
This highlights the strangeness of Peter’s expression. We speak of voices carrying, but never of carrying voices. Who carried the voice of the Father? Why does God’s voice need to be carried? The answer to such questions is revealed in verse 21.
Who carried the voice of the Father to the Son on the mount of transfiguration? The same person who carried the voice of the Father to prophets speaking God’s word: the Holy Spirit. In verse 21 Peter uses the same verb he used in verses 17 and 18—phero. Granted the imagery has changed a bit. In verses 17 and 18 the voice of God is carried while in verse 21 men are carried. But in both cases, the end result is the same. If it is not for the work of the Holy Spirit, man is not able to properly receive the word of God.
If the Holy Spirit had not given Peter, James, and John understanding on the holy mountain, they would not have comprehended the sound (cf. John 12:28-29; Acts 22:29). If the prophets had not been carried, they could not have spoken from God. At the Transfiguration and in the Old Testament the Holy Spirit had one objective: to declare to men the love of the Father for the Son (cf. 1 Peter 1:10-12).