Charles Ellicott Commentary John 14:20

"In that day ye shall know that I am in my Father, and ye in me, and I in you." — John 14:20 (ASV)

At that day ye shall know—that is, the day of the gift of the Comforter, in whom Christ shall come to them. In the first reference, the Day of Pentecost is meant, but the words also apply to every spiritual quickening and will apply to the final coming in the last day. The pronoun “ye” is emphatic—“You shall know for yourselves.”

That I am in my Father, and ye in me, and I in you.—Compare the note on John 10:38. The result of this spiritual illumination would be that they would know for themselves the immanence of the Son in the Father, and their own union with the Father through Him. They ask now (John 14:8) for a manifestation of the Father.

The Spirit would so bring the life of Christ to their hearts that they would read in it the manifestation of the Father, and feel that in and through that life their own spirit has communion with God. The Spirit would witness with their spirit that they were the children of God. They would seek no longer for a Theophany from without, but in the depth of their inmost lives would cry, “Abba, Father.”