John Gill Commentary 2 Chronicles 15:7

"But be ye strong, and let not your hands be slack; for your work shall be rewarded." — 2 Chronicles 15:7 (ASV)

Be you strong therefore, and let not your hands be weak
Be hearty, earnest, and vigorous, and not languid and remiss in reforming the worship of God, which Asa had begun:

for your work shall be rewarded ;
with peace and prosperity at home, and success against enemies abroad, of which they had had a recent instance.