Chapter 4, Mishnah 9. Having dealt in the previous Mishnah with the six things the people of Yericho did, our Mishnah now lists six things that King Chizkiyahu did: three of them the Sages agreed with, and three of them they disagreed with.
Three acts that the Sages agreed with:
"Girer atzmos aviv al mitah shel chavalim" - he took the bones of his father, who was wicked, and dragged them on a bed made of ropes, which was considered a disgrace. He had two intentions in doing this: first, since his father was wicked, the disgrace done to him serves as a form of atonement; and second, so that people would know that wicked people are treated with disgrace, and through this the Name of the Holy One, blessed is He, would be sanctified.
"Kitas nechash hanechoshes" - the copper snake was made by Moshe Rabbeinu, when the snakes bit the Jewish people in the wilderness after they complained about the manna. The Holy One, blessed is He, commanded that it be made, and whoever looked at it was healed. But over the course of time people began to worship it, and therefore Chizkiyahu ground it up so that it would not serve as an object of idolatry.
"Ganaz sefer refuos" - a book that contained a cure for every illness. Chizkiyahu sensed that this was not good for the people spiritually, since they would not pray to Hashem: when they became ill, they would look in the book and treat their illness that way. He therefore hid it away, and the Sages agreed with him.
Three acts that they did not agree with:
"Kitzetz dalsos haheichal" - in order to appease the king of Ashur and prevent him from attacking, he cut off the doors of the Sanctuary in the Beis HaMikdash and sent them to him as tribute. The Sages did not agree with him, since they saw this as excessive submission; he should not have done so, but rather should have placed greater trust in Hashem.
"Sasam mei Gichon" - he stopped up the waters of the Gichon river, which are the upper waters. This act caused hardship for the public, since from then on the water supply was reduced, whereas he should have trusted in Hashem. The prophet told him to trust in Hashem, since He would protect the city of Yerushalayim in his time.
"Ibeir Nisan b'Nisan" - he made the year a leap year by adding a second Adar too late. The second Adar must be added while it is still Adar, and the Gemara clarifies that he did not do it in Nisan itself, but on the thirtieth day of Adar. That day could have been Rosh Chodesh Nisan: had Adar been a month of twenty nine days, the thirtieth day would have been Rosh Chodesh Nisan. And since it had the potential to be Rosh Chodesh Nisan, it was not proper for him to begin making the year a leap year at such a late point, and therefore they did not agree with him. Even so, the Mishnah uses the expression that he made Nisan a leap year in Nisan.
In summary: in this Mishnah we listed six acts of King Chizkiyahu. Three that the Sages agreed with: dragging the bones of his wicked father for the sake of atonement and sanctifying Hashem's Name, grinding up the copper snake that had become an object of idolatry, and hiding away the book of cures that led to the neglect of prayer. And three that they did not agree with: cutting off the doors of the Sanctuary and sending them to the king of Ashur out of excessive submission instead of trusting in Hashem, stopping up the waters of the Gichon, which caused hardship for the public even though he had been told to trust in Hashem, and making the year a leap year on the thirtieth day of Adar, a day that had the potential to be Rosh Chodesh Nisan.