John 8:28

Then said Jesus unto them Better, as so often (see on John 8:21), Therefore said Jesus, i.e. in consequence of their gross want of perception. -Unto them" is of doubtful authority.

When ye have lifted up On the Cross: comp. John 3:14 and John 12:32. The Crucifixion was the act of the Jews, as Peter tells them in Solomon's Porch (Acts 3:13-15).

then shall ye know Better, then shall ye perceive. It is the same verb as is used in John 8:27, and evidently refers back to that (comp. John 8:43). Had they known the Messiah they would have known His Father also (John 14:9). But when by crucifying Him they have brought about His glory, then and not till then will their eyes be opened. Then will facts force upon them what no words could teach them. Comp. John 12:32.

that I am he See on John 8:24.

but as my Father hath taught me Better, but that as My Father taught Me, i.e. before the Incarnation; aorist, not perfect, like -heard" in John 8:26. The construction depending on -then shall ye understand" continues to the end of this verse, and possibly down to -is with Me."