They understood (perceived) not that he spake to them of the Father. This difficult parenthesis of the evangelist calls attention to the fact that, during the immediately preceding discourse and controversy, Jesus had dropped his references to the Father, and had used the periphrasis, "he that sent me," probably suggesting to this strangely excited populace, fed with weird fancies and wild expectations, that the mysterious Being with whom they were conversing was but the Delegate of One mightier than he, who was hidden in the secret place of God's providence until the hour of his own manifestation should appear to have struck.
They might have remembered the utter deference which the great prophet John had displayed before a Messiah whom as yet they knew not. They may have heard that even John himself, at a later date, sent from the prison two of his disciples to propound the query, "Art thou he that should come, or do we look for another?"
in other words, "Art thou the final Manifestation of all that I have predicted and believed? or is another to make his appearance with fire and axe and available force to compel obedience and to secure universal homage?"
It is more than probable that the evangelist, being personally alive to the cross currents of passion, enthusiasm, and hostility which were at work in the hearts of the populace, saw by the very blankness and confusion on their faces, and the "asides" of the multitude, that they had not perceived that Jesus was throughout in these references speaking of the Father of all—the supreme Source of all power, the Lord of hosts.
Even when he had said, "Ye have not known me, nor my Father," they had not risen to such a conception of the Lord's meaning as to suppose that the supreme Father himself was being suggested to them and cited as the corroborative Witness, as the supernatural Aid and Divine Presence which was giving validity to all that Christ has said about himself.
Their ignorance and lack of perception need not astonish us when we reflect upon the obscurity and non-receptivity of the apostles themselves, and the like obtuseness of theologians and cultivated men of the world in every age from that day to this.
The remark is, moreover, added doubtless to interpret the following verses, in which the ideas of verse 26 are repeated, with the difference that, whereas he had already spoken of him that sent him, and who had authorized his words and judgments, Jesus now gives to him the beloved name of "the Father."