A.T. Robertson Commentary John 16:28

"I came out from the Father, and am come into the world: again, I leave the world, and go unto the Father." — John 16:28 (ASV)

I came out from the Father (εξηλθον εκ του πατρος). Definite act (aorist), the Incarnation, with repetition of εκ (out of), while in verse 27 we have παρα του πατρος εξηλθον) with no practical distinction between εκ and παρα in resultant idea.

Am come (εληλυθα). Perfect active indicative of ερχομα, as in 18:37. The Incarnation is now a permanent fact, once only a blessed hope (11:27). His leaving the world and going to the Father does not set aside the fact of the Incarnation. Both αφιημ (I leave) and πορευομα (I go) are futuristic present indicatives.