William Burkitt on 2 Peter 1:16

Our apostle comes now to exhort them to constancy in the faith of the gospel, assuring them that himself and his fellow-apostles had not followed artificially devised fables, when they made known to them the coming of Christ in the flesh, and that he was truly, and in very deed, the promised Messias; for that he himself, with James and John, were with Christ upon mount Tabor, as eye-witnesses of his transfiguration, where and when he received in his human nature a communicated splendor, and God the Father from heaven, the seat of the magnificent glory, pronounced him to be his well-beloved Son, in whom he is well-pleased.

Learn hence, that God the Father's testimony from heaven, concerning his Son Jesus Christ, did effectually bring honour and glory unto Christ, and is a great obligation upon us to faith and obedience to him; He received from God the Father honour and glory, attesting him to be his well-beloved Son.

Learn, 2. That there was as much assurance given of the certainty of Christ's being the promised Messias, and of the truth of the evangelical doctrine, as the world could reasonably desire. Men can humanly be certain of nothing more than what they perceive by their senses, which are the proper judges of all sensible objects; now no satisfaction of this kind was wanting to the world concerning our blessed Saviour and his miracles: The apostles attesting what they had heard, what they had seen with their eyes, and their hands had handled of the word of life, 1John 1:1