Isaiah 38:4 - Albert Barnes' Notes on the Bible

Then came the word of the Lord - In the parallel place in 2 Kings 20:4, it is said, ‘And it came to pass, afore Isaiah was gone out into the middle court, that the word of the Lord came unto him.’ That is, the message of God name to Isaiah before he had left Hezekiah; or as soon as he had offered his prayer. This circumstance is omitted by Isaiah on the revision of his narrative which we have before us. But there is no contradiction. In this place it is implied that the message came to him soon, or immediately.