Matthew Henry Commentary 2 Chronicles 26:16-23

"But when he was strong, his heart was lifted up, so that he did corruptly, and he trespassed against Jehovah his God; for he went into the temple of Jehovah to burn incense upon the altar of incense. And Azariah the priest went in after him, and with him fourscore priests of Jehovah, that were valiant men: and they withstood Uzziah the king, and said unto him, It pertaineth not unto thee, Uzziah, to burn incense unto Jehovah, but to the priests the sons of Aaron, that are consecrated to burn incense: go out of the sanctuary; for thou hast trespassed; neither shall it be for thine honor from Jehovah God. Then Uzziah was wroth; and he had a censer in his hand to burn incense; and while he was wroth with the priests, the leprosy brake forth in his forehead before the priests in the house of Jehovah, beside the altar of incense. And Azariah the chief priest, and all the priests, looked upon him, and, behold, he was leprous in his forehead, and they thrust him out quickly from thence; yea, himself hasted also to go out, because Jehovah had smitten him. And Uzziah the king was a leper unto the day of his death, and dwelt in a separate house, being a leper; for he was cut off from the house of Jehovah: and Jotham his son was over the king`s house, judging the people of the land. Now the rest of the acts of Uzziah, first and last, did Isaiah the prophet, the son of Amoz, write. So Uzziah slept with his fathers; and they buried him with his fathers in the field of burial which belonged to the kings; for they said, He is a leper: and Jotham his son reigned in his stead." — 2 Chronicles 26:16-23 (ASV)

The transgression of the kings before Uzziah was forsaking the temple of the Lord and burning incense upon idolatrous altars. But his transgression was going into the holy place and attempting to burn incense upon the altar of God. See how hard it is to avoid one extreme and not run into another. Pride of heart was at the bottom of his sin, a lust that ruins many.

Instead of lifting up God's name in gratitude to Him who had done so much for him, his heart was lifted up to his own harm. People's pretending to forbidden knowledge and seeking things too high for them stem from pride of heart. The incense of our prayers must, by faith, be put into the hands of our Lord Jesus, the great High Priest of our profession; otherwise, we cannot expect it to be accepted by God (Revelation 8:3). Though Uzziah strove with the priests, he would not strive with his Maker.

But he was punished for his transgression; he remained a leper until his death, shut out from society. The punishment corresponded to the sin, as clearly as a face is reflected in a mirror. Pride was at the bottom of his transgression, and thus God humbled him and dishonored him. Those who covet forbidden honors forfeit allowed ones.

Adam, by grasping for the tree of knowledge which he was forbidden to eat from, barred himself from the tree of life which he could have eaten from. Let all who read say, The Lord is righteous. And when the Lord sees fit to throw prosperous and useful people aside as broken vessels, if He raises up others to fill their places, they can rejoice to renounce all worldly concerns and employ their remaining days in preparation for death.