2 Peter 1:17

17. For he received from God the Father. He chose one memorable example out of many, even that of Christ, when, adorned with celestial glory, he conspicuously displayed his divine majesty to his three disciples. And though Peter does not relate all the circumstances, yet he sufficiently designates them when he says, that a voice came from the magnificent glory. For the meaning is, that nothing earthly was seen there, but that a celestial majesty shone on every side. We may hence conclude what those displays of greatness were which the evangelists relate. And it was necessarily thus done, in order that the authority of that voice which came might be more awful and solemn, as we see that it was done all at once by the Lord. For when he spoke to the fathers, he did not only cause his words to sound in the air, but by adding some symbols or tokens of his presence, he proved the oracles to be his.

This is my beloved Son. Peter then mentions this voice, as though it was sufficient alone, as a full evidence for the gospel, and justly so. For when Christ is acknowledged by us to be him whom the Father has sent, this is our highest wisdom. There are two parts to this sentence. When he says, “This is,” the expression is very emphatical, intimating, that he was the Messiah who had been so often promised. Whatever, then, is found in the Law and the Prophets respecting the Messiah, is declared here, by the Father, to belong to him whom he so highly commended. In the other part of the sentence, he announces Christ as his own Son, in whom his whole love dwells and centres. It hence follows that we are not otherwise loved than in him, nor ought the love of God to be sought anywhere else. It is sufficient for me now only to touch on these things by the way.