Adam Clarke on John 14:28

I go away - To the Father by my death:

And come again unto you - By my resurrection.

Ye would rejoice - Because, as the Messiah, I am going to receive a kingdom, and power, and glory, for ever. Therefore as my friends ye should rejoice in my elevation, though for a while it may put you to the pain of being separated from me: besides, I am going that I may send you the Holy Spirit, which shall fill you with the fullness of God: on your own account, therefore, ye should have rejoiced and not mourned.

My Father is greater than I - In Joh 14:24, Christ tells his disciples that the Father had sent him: i.e. in his quality of Messiah, he was sent by the Father to instruct, and to save mankind. Now, as the sender is greater than the sent, Joh 13:16, so in this sense is the Father greater than the Son; and in this sense was the passage understood by Origen, Jerome, Novatian, and Vigilius, who read the text thus: The Father, ὁ πεμψας, who sent me, is greater than I. It certainly requires very little argument, and no sophistry, to reconcile this saying with the most orthodox notion of the Godhead of Christ; as he is repeatedly speaking of his Divine and of his human nature. Of the former he says, I and the Father are one, Joh 10:30; and of the latter he states, with the same truth, The Father is greater than I.