Albert Barnes Commentary Isaiah 39:4

"Then said he, What have they seen in thy house? And Hezekiah answered, All that is in my house have they seen: there is nothing among my treasures that I have not showed them." — Isaiah 39:4 (ASV)

What have they seen?—It is probable that the fact that Hezekiah had shown them the treasures of his kingdom was known in Jerusalem. Such a fact would be likely to attract attention and to produce inquiry among the people about the cause.

All that is in mine house—Here was the confession of a frank, an honest, and a pious man. There was no concealment; no disguise. Hezekiah knew that he was dealing with a man of God—a man to whom he had also been under great obligations. He knew that Isaiah had come commissioned by God, and that it would be in vain to attempt to conceal anything. Nor does he seem to have wished to make any concealment. If he was conscious that what he had done had been improper, he was willing to confess it; and at any rate, he was willing that the exact truth should be known. Had Hezekiah been like Ahaz, he might have spurned Isaiah from his presence for presenting improper inquiries.

But Hezekiah was accustomed to regard with respect the messengers of God, and he was therefore willing to submit his whole conduct to the divine adjudication and reproof. Piety makes a man willing that all that he has done should be known. It saves him from double-dealing and subterfuges, and a disposition to make vain excuses; and it inclines him to fear God, to respect his ambassadors, and to listen to the voice of eternal truth.