Albert Barnes on Matthew 26:37

And he took with him Peter and the two sons of Zebedee. That is, James and John, Mt 10:2. On two other occasions he had favoured these disciples in a particular manner, suffering them to go with him to witness his power and glory, viz., at the healing of the ruler's daughter, (Lk 8:51,) and at his transfiguration on the mount, Mt 17:1.

Sorrowful. Affected with grief.

Very heavy. The word in the original is much stronger than the one translated sorrowful. It means, to be pressed down, or overwhelmed with great anguish. This was produced, doubtless, by a foresight of his great sufferings on the cross in making an atonement for the sins of men.