Hezekiah's father, King Ahaz, was guilty of shutting down the temple (2nd Chronicles 28:24). Imagine not having a place to go for worship! Praise the Lord, his son was willing to undo what his foolish father had accomplished. These 2 men were kings in Judah during the same period of time that the Assyrians were mopping up the Northern Kingdom of Israel. Who knows, perhaps the judgment of God against Israel was partly influential in keeping good King Hezekiah on the straight and narrow?
Anyway, Hezekiah spent about 3 decades ruling over Judah. And, according to this chapter his main accomplishment was the restoration of the use of the temple (2nd Chronicles 29:3, 5, 15, 16 - 18, 20, 21, 31 & 35). Not just any use, of course; for the proper use; for the worship of Jehovah. He wanted a fresh commitment between his people and God. He wanted a commitment from them to remain loyal to God (II Chronicles 29:10). The experience of God's discipline against them had been sufficient to convince Hezekiah that he and his people needed to learn to be faithful (2nd Chronicles 29:9).
Essentially, we can say that Hezekiah brought a spiritual revival to Jerusalem and Judah. He couldn't and didn't do it alone though. 2nd Chronicles 29:34 speaks of some Levites who were "upright in heart'' - men who "sanctified themselves" for religious service. Additionally, 2nd Chronicles 29:36 says that "God prepared the people" for this revival. Only God can bring true revival (Ezra 9:8).