Note 22 at Jn. 14:13: If the previous promise didn't convince the disciples that the Father would accomplish the same miracles through them as He had through Jesus, then this one should. Jesus reiterates the truth of verse 12 in different words, thereby underscoring the certainty of this promise. Then in the next verse, He repeats this same promise again.

This is very uncharacteristic of Jesus to repeat Himself three times in immediate succession and must, no doubt, be interpreted as Jesus assuring His disciples that this seemingly unbelievable promise was, in fact, true. As explained in Hebrews 6:17-18, God did the same thing with Abraham. Anyone who would doubt the statement of verse 12 because of it being such a departure from the "norm," could not in a pure heart doubt the meaning of these three statements of Jesus when taken as a whole.