King Asa lived a life that was honorable to God, he seemed to want to do everything right, the way God wanted. He trusted in God, who helped him win a battle against what looked like an unbeatable foe. He also removed foreign alters and pagan shrines.
But as he lived his life and ruled as king, he slipped towards the end and stopped trusting in God, and stopped seeking help from the Lord. He reigned for 41 years, living for God most of that time.
We need to be careful that we finish strong, and don't go out on a bad note after many years of living for God. Spending more time in prayer as we get older is a good start.