Isaiah 37:21-22

The Lord explained that it was Hezekiah’s trust in Him, expressed through his prayer, that led to his receiving information about what He would do. Hezekiah would see the Lord’s hand at work more clearly because he had prayed.

Assyria had mocked a "person" who was especially dear to the Lord, namely, His "virgin daughter," Jerusalem (cf. Isaiah 1:8; Isaiah 47:1). No foreign foe had penetrated Jerusalem. Thus Assyria had incurred His anger.