Charles Ellicott Commentary 2 Kings 18:7

"And Jehovah was with him; whithersoever he went forth he prospered: and he rebelled against the king of Assyria, and served him not." — 2 Kings 18:7 (ASV)

And he prospered ... went forth. — Whithersoever he would go forth he would prosper. (The italicized and is needless here, as in 2 Kings 18:6.)

Prospered. — Compare 1 Kings 2:3; Proverbs 17:8. Going forth denotes any external undertaking or enterprise, especially going forth to war. (Compare the phrase “going out and coming in.”)

He rebelled against the king of Assyria — i.e., refused the tribute which Ahaz his father had paid. In this matter also it is implied that Hezekiah succeeded. The mention of Hezekiah’s revolt here does not imply that it happened at the beginning of his reign, for 2 Kings 18:1–12 are a preliminary sketch of his entire history. The subject here glanced at is continued at large in 2 Kings 18:13 and following.