Now are we sure that thou knowest all things. — Comp. John 16:19; John 16:23. The “now” is emphatic, as in the previous verse. They see in His present knowledge of their thoughts, and in the light which has come to them from the statements of John 16:28, the fulfilment of the promise which He has made for the future (John 16:23). They think that the day has already come when they shall ask Him nothing, for He knows all things, and communicates to them the fulness of truth.
By this we believe that thou camest forth from God. — They had believed this before (John 16:27), but here, as frequently, St. John remembers the development of their faith. (Comp. Note on John 2:11.) They find, in His knowledge of their thoughts (John 16:19), and in the full solution which He gives to their difficulties, ground for a new faith; and upon this new proof of His divinity they have a new faith in Him. (Comp. the instance of Nathanael’s faith at the end of John 1)