William Burkitt on John 5:37

Here our blessed Saviour produces again the testimony of his Father, that he was the true and promised Messias: this was given him both at his baptism and his transfiguration: when God the Father owned Christ to be his Son, by an audible voice from heaven, saying, This is my beloved Son in whom I am well pleased. Which testimony the Jews ought the more to have regarded, because though their forefathers had heard the voice of God at certain times, Exod 20:1; Deut 4:1 yet they in their times had never heard his voice.

Learn hence, That the Father's immediate testimony of Christ from heaven, is greater than all the testimonies given to him here on earth; greater than John's, greater than his miracles. The presence of the glorious Trinity, when that testimony was given, Matt 3:1-17 ult. made that witness most awful and solemn.