2 Chronicles 15:4

But when they in their trouble did turn unto the LORD God of Israel, and sought him, he was found of them.

When they were in trouble they turned to the Lord God of Israel and sought Him, and He was found by them and made Himself available to them. Seeking God in this way brings His presence and His help. This turning came after Israel had been for a long time without the true God and without true worship and instruction.

For Asa and Judah this turning meant remaining with the Lord, seeking Him, and being strong in their work. Asa responded by leading a reform, and the people entered into a wholehearted covenant to seek God, He was found by them and gave them rest. The verse encourages those who have forsaken God or have grown cold and backslidden to seek Him with the assurance that He will be found. He promises to be found by those who seek Him with their whole heart.