What he didn’t say: “Kick back and relax. There will be another time to build the temple.”
The Israelites would be able to look at what they did while they were strong and gain strength in their upcoming times of weakness.
Same for us. There isn’t time for us to be idle in the Lord. We need to be laying our own stepping stones of encouragement against times to come. If we’re working in times of peace it’s to benefit ourselves, those around us and to give God glory.