John 5:36-38 — But I have greater witness than that of John: for the works which the Father hath given Me to finish, the same works that I do, bear witness of Me, that the Father hath sent Me.
And the Father Himself, which hath sent Me, hath borne witness of Me. Ye have neither heard His voice at any time, nor seen His shape.
And ye have not His word abiding in you: for whom He hath sent, Him ye believe not.
Christ performed miracles, which should have convinced the Jews that God had sent Him, as it did Nicodemus. (John 3:2; John 10:25)
The Father gave direct witness of the Son three times:
- His baptism — Matthew 3:16-17
- On the Mount of Transfiguration — Matthew 17:5
- Before His crucifixion — John 12:28
The Jewish leaders had never heard nor seen God's witness, but they had seen and heard the Son (Hath in these last days spoken unto us by His Son, whom He hath appointed heir of all things, by whom also He made the worlds — Hebrews 1:2) and they still didn't believe.
They read the Scriptures, but didn't have it in their hearts.