| Barnes' Notes on the Bible They understood not - They knew not, or they were unwilling to receive him as a messenger from God. They doubtless understood that he meant to speak of God, but they were unwilling to acknowledge that he really came from God.
Gill's Exposition of the Entire BibleThey understood not that he spake to them of the Father. That sent him, and who was true and faithful to all he had said, whether in a way of promise, or threatening; such was their stupidity, that they did not know that he meant God the Father by him that sent him, so deriving his mission and doctrine from him; their hearts were made fat, and hardened, and their eyes were blinded. The Vulgate Latin version reads, "they did not know that he said, God was his Father"; and so Beza's most ancient copy, and another exemplar of his.
Vincent's Word StudiesThey understood (ἔγνωσαν) Perceived, as Rev. He spake Imperfect. Was speaking would be much better.
Geneva Study Bible{11} They understood not that he spake to them of the Father. (11) Even the contempt of Christ results in his glory: and this thing his enemies will eventually feel to their great pain.
Wesley's Notes 8:27 They understood not - That by him that sent him he meant God the Father. Therefore in John 8:28,29 he speaks plainly of the Father, and again claims the Divine name, I AM.
Matthew Henry's Concise Commentary8:21-29 Those that live in unbelief, are for ever undone, if they die in unbelief. The Jews belonged to this present evil world, but Jesus was of a heavenly and Divine nature, so that his doctrine, kingdom, and blessings, would not suit their taste. But the curse of the law is done away to all that submit to the grace of the gospel. Nothing but the doctrine of Christ's grace will be an argument powerful enough, and none but the Spirit of Christ's grace will be an agent powerful enough, to turn us from sin to God; and that Spirit is given, and that doctrine is given, to work upon those only who believe in Christ. Some say, Who is this Jesus? They allow him to have been a Prophet, an excellent Teacher, and even more than a creature; but cannot acknowledge him as over all, God blessed for evermore. Will not this suffice? Jesus here answers the question. Is this to honour him as the Father? Does this admit his being the Light of the world, and the Life of men, one with the Father? All shall know by their conversion, or in their condemnation, that he always spake and did what pleased the Father, even when he claimed the highest honours to himself. | 
