A.T. Robertson Commentary John 3:33

"He that hath received his witness hath set his seal to [this], that God is true." — John 3:33 (ASV)

Hath set his seal (εσφραγισεν). First aorist active indicative of σφραγιζω for which verb see Mt 27:66. The metaphor of sealing is a common one for giving attestation as in 6:27. The one who accepts the witness of Jesus attests that Jesus speaks the message of God.