A.T. Robertson Commentary John 14:28

"Ye heard how I said to you, I go away, and I come unto you. If ye loved me, ye would have rejoiced, because I go unto the Father: for the Father is greater than I." — John 14:28 (ASV)

I go away, and I come (υπαγω κα ερχομα), both futuristic presents (7:33; 14:3,18).

If ye loved me (ε ηγαπατε με). Second-class condition with the imperfect active of αγαπαω referring to present time, implying that the disciples are not loving Jesus as they should.

Ye would have rejoiced (εχαρητε αν). Second aorist passive indicative of χαιρω with αν, conclusion of second-class condition referring to past time, "Ye would already have rejoiced before this" at Christ's going to the Father (verse 12).

Greater than I (μειζων μου). Ablative case μου after the comparative μειζων (from positive μεγας). The filial relation makes this necessary. Not a distinction in nature or essence (cf. 10:30), but in rank in the Trinity. No Arianism or Unitarianism here. The very explanation here is proof of the deity of the Son (Dods).