Asa was king of Judah for 41 years (I Kings 15:10). It was a long and prosperous period in the history of the southern tribes. As Israel waned and dwindled, Judah grew stronger. Mercifully God had ended Asa's father's reign after a short 3 year term. Abijam (Asa's father) had not been a good king, yet, for David's sake, God allowed his son to reign (I Kings 15:4).
Some of the good things that Asa did are listed briefly in this chapter. He put a stop to the homosexual nonsense. He destroyed the idols that had accumulated in the land. He even dealt with the sin that was in his own family. His mother had taken a leading role in the spiritual adultery of the nation, so he removed her from her position as a head of state... and he destroyed her idolatrous worship center too. He even gathered valuable things again into the temple to replace some of those things which had been removed by the Egyptians during the reign of his grandfather, Rehoboam.
Admittedly, Asa wasn't perfect, but his heart certainly was (I Kings 15:14). We will study in Chronicles how he made some poor decisions at the end of his life; decisions which ended up costing him some... although, at least it wasn't enough to tarnish his overall reputation as a godly king. One of his mistakes was that instead of just trusting God to be his protector, he hired the Syrians to help him against Israel. And, he used God's money to hire those mercenaries?