“is not he the one whose high places and whose altars Hezekiah has taken away.” Sennacherib was very well informed about what was going on in Judah, and it is almost certain that he had spies there and/or had other sources of information, after all, he had already conquered a large number of the cities of Judah and would have learned a lot from the people he captured (2 Kings 18:13). So what he said was not a guess. Hezekiah had taken away the high places and pagan altars (2 Kings 18:3-4), and told the people to worship in Jerusalem. Hezekiah had also told his people and his army that they were to trust in Yahweh (2 Chron. 32:8). Hezekiah’s reform was so extensive, and his life and actions so important, that 2 Chronicles has four chapters on Hezekiah (2 Chron. 29-32).
The ungodly and pagan acts of king Ahaz, Hezekiah’s father, would have penetrated the culture quite deeply in the 16 years of Ahaz’s reign. So when Hezekiah abruptly put an end to those pagan practices he would have upset quite a few people. That meant that the reforms of Hezekiah, although welcomed by the godly people of Judah, would have been hated and opposed by the ungodly people. This was one of those situations where the leader cannot please everyone. Hezekiah did what he knew was right, and did it in spite of the fact that it would have upset and angered many people, and so Hezekiah would have been pressured and perhaps even threatened because of his reforms.
Also, this verse reveals both that Sennacherib the king of Assyria misunderstood Hezekiah’s reform, and that there was syncretism and perversion of the worship of Yahweh going on in the cities of Judah. God had commanded that He was to be worshipped “in the place that Yahweh your God will choose” (Deut. 12:1-14), and He chose Jerusalem. But the people ignored that command and worshipped God in many different places—and “worshipped” meant that they sacrificed, performed rituals, etc., in many different places. Furthermore, much of that service and “worship” would have involved people who were not Levitical priests and also involved practices borrowed from the worship of pagan gods. The people may have thought they were worshipping Yahweh, but in reality they were being disobedient and ungodly. Nevertheless, when Hezekiah put a stop to the ungodly worship, Sennacherib naturally concluded that Hezekiah was being tyrannical by insisting that everyone come to worship in the city where he lived, Jerusalem, and to the temple where he worshipped. It is quite possible that Sennacherib thought that if he communicated directly with the people of Jerusalem that he could start a popular uprising against Hezekiah and take the city without a fight, and he tried that tactic (cp. 2 Kings 18:25-35). Thankfully, that tactic did not work.