Now they have known. Here our Lord expresses what is the chief part in faith, which consists in our believing in Christ in such a manner, that faith does not rest satisfied with beholding the flesh, but perceives his Divine power. For when he says, They have known that all things which thou hast given me are from thee, he means, that believers feel that all that they possess is heavenly and divine. And, indeed, if we do not perceive God in Christ, we must remain continually in a state of hesitation.

They have known - They have been taught that and have believed it.
Hast given me - This refers, doubtless, to the doctrine of Christ, John 17:8. They are assured that all my instructions are of God.

Now they have known,.... The Syriac version reads it "I have known"; and so the Persic and Gothic versions, contrary to most copies and other versions, which read, as we render, "they have known", that is, the disciples and apostles of Christ:
that all things whatsoever thou hast given me; all temporal things, the world and the fulness of it; all power in heaven, and in earth, or a power of disposing of all things for his own service, as Mediator; all spiritual things, the covenant of grace, with all its blessings and promises, the Spirit of God, with all his, gifts and graces, a fulness of all grace for his people, yea, eternal life and glory; and everything relating to his mediatorial office and character, power to perform miracles, knowledge and wisdom to preach the Gospel, strength to procure the salvation of his people; every thing to qualify him for the government of church and the judgment of the world:
are of thee; owing to his good will and pleasure, by his appointment and constitution, as an instance of love to him, and that he might, as man, and Mediator, be honoured, and in all things have the pre-eminence, and all for the good of his chosen ones: now the knowledge of this by his disciples, must greatly confirm the mission of Christ, render him very suitable to them, cause them to entertain a greater esteem for him, lead them into some admiring views of the grace of God, in giving so much into Christ's hands for them, and engage them the more cheerfully to obey his commands.

Now they know that all things - Which I have done and spoken, are of thee - And consequently right and true.