John Gill 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)

Then said he, what have they seen in your house ?
&c.] Coming nearer to the point he had in view, and which was the thing that was displeasing to the Lord; not that he had received the ambassadors, and used them in such a manner as persons in such a quality ought to be used; but that he had shown them what he ought not to have done, and especially from such a principle of pride and vanity as he did:

and Hezekiah answered
without any reserve, very openly, not suspecting that the prophet was come with a reproof to him, or to blame him, or would blame him for what he had done:

all that is in my house have they seen ;
the several royal apartments, and the furniture of them:

there is nothing among my treasures that I have not showed them :
which were more secret, laid up in cabinets, under lock and key; his gold, silver, jewels, and precious stones, spices, and ointments.

Jerom thinks he showed them the furniture and vessels of the temple, though he does not mention them.