A.T. Robertson Commentary John 6:38

"For I am come down from heaven, not to do mine own will, but the will of him that sent me." — John 6:38 (ASV)

I am come down (καταβεβηκα). Perfect active indicative of καταβαινω. See on 33 for frequent use of this phrase by Jesus. Here απο is correct rather than εκ with του ουρανου.

Not to do (ουχ ινα ποιω). "Not that I keep on doing" (final clause with ινα and present active subjunctive of ποιεω).

But the will (αλλα το θελημα). Supply ινα ποιω after αλλα, "but that I keep on doing." This is the fulness of joy for Jesus, to do his Father's will (4:34; 5:30).