2 Chronicles 28:20,21 - Joseph Benson’s Commentary on the Old and New Testaments

Tilgath-pilneser came and distressed him By quartering the Assyrian soldiers upon his country, by growing insolent and imperious, and creating him a great deal of vexation, and by proving as a broken reed, which not only fails him that leans upon it, but pierces his hand. Or, straitened him, (as יצר, jatsar, rather signifies,) namely, by robbing him of his treasures. For Ahaz took away a portion, &c. He pillaged the house of God, and the king's house, and pressed the princes for money to hire these foreign forces into his service. For though he had conformed to the idolatry of these his heathen neighbours, they did not value or love him the more for that; nor did his compliance, by which he lost God, gain them; nor could he make any interest with them but by his money. Thus it is generally found that wicked men have no real affection for those that revolt to them, nor care to do them a kindness. But he strengthened him not A most emphatical expression: for though he weakened his present enemy, the Syrian, as is related 2 Kings 16:9, taking Damascus, and carrying the people away captive; yet really, all things considered, he did not strengthen Ahaz and his kingdom. He did not help him to recover the cities which the Philistines had taken from him; nor did he lend him any forces, or enable him to recruit his own. On the contrary, he weakened him; for by removing the Syrian, who, though a troublesome neighbour, was a kind of bulwark to him, and by destroying Samaria, he opened a way for the invasion of his country with more facility, as happened in the very next reign.