They understood not - It is remarkable that they did not understand Jesus in this, but it shows how slow persons are to believe. Even his parents, after all that had taken place, did not seem to comprehend that "he" was to be the Saviour of people, or if they did, they understood it in a very imperfect manner.

And they understood not the saying,.... What he meant by his Father's house, or his Father's business, and the necessity of his being there, and about that:
which he spake unto them; at that time, and as above related.

understood not--probably He had never expressly said as much, and so confounded them, though it was but the true interpretation of many things which they had seen and heard from Him at home. (See on John 14:4.) But lest it should be thought that now He threw off the filial yoke, and became His own Master henceforth, and theirs too, it is purposely added, "And He went down with them, and was subject unto them." The marvel of this condescension lies in its coming after such a scene, and such an assertion of His higher Sonship; and the words are evidently meant to convey this. "From this time we have no more mention of Joseph. The next we hear is of his "mother and brethren" (John 2:12); whence it is inferred, that between this time and the commencement of our Lord's public life, Joseph died" [ALFORD], having now served the double end of being the protector of our Lord's Virgin--mother, and affording Himself the opportunity of presenting a matchless pattern of subjection to both parents.

Understood not. Did not comprehend all he meant in speaking of his Father's house.

It is observable that Joseph is not mentioned after this time; whence it is probable, he did not live long after.