At first, it may seem puzzling to have books like 1 & 2 Chronicles in the Bible, because they cover events already covered in other books, such as 1 & 2 Kings. However, the reason for such duplication can be summed up in one word: perspective. 1 & 2 Kings were written during the judgment of the Jewish exile, to explain why the Israelites, who had a unique covenant with the only true God, were in captivity. It was because of their longstanding sins of idolatry, oppression, greed, and the like, from which they refused to repent.
1 & 2 Chronicles (which were originally one book, broken into two when translated into Greek, which required more space and hence two scrolls instead of one) was written after the exile of the Southern Kingdom of Judah, when the Jews had returned to their land and faced the daunting task of rebuilding the temple, its worship, and their lives as a nation under God. Instead of reproof, they now needed encouragement. They needed to know that they had both an inspiring history of God's working in their past, and a bright future, if they would worship and serve God rightly in obedience and reverence.
For this reason Chronicles emphasizes right worship, and revivals that took place when leaders and the people returned to God in humility and repentance. God had not forgotten his people, and would show them His faithfulness again if they would align themselves with His Word.
The probable author (or compiler from various sources) is the scribe Ezra, described in the book of Ezra. From that book we know that Ezra had a passion for holiness among his people, and stirring present obedience by remembering past history was no doubt an important purpose for his producing this portion of Scripture. His purpose is well summarized in one of Chronicles' most famous verses:
If my people who are called by My name will humble themselves, and pray and seek My face, and turn from their wicked ways, then I will hear from heaven, and will forgive their sin and heal their land. - 2 Chronicles 7:14-15
Have you wandered from the Lord in any way in your life? Have you tasted the bitterness of the results of that? Then know from the book of Chronicles that there is a way back: humble yourself, pray, seek His face, and turn from any sin in your life, large or small. That's your part, and when you have done it, He will do His: He will hear, forgive, and heal you.