This verse completes the pair begun at Proverbs 10:4.
Quick answer
Diligence is not only effort; it is timing. Harvest does not wait, and the son who sleeps through it loses what no later work can recover.
Read both lines
Where verse 4 watched the hands, this verse watches the calendar. Summer and harvest are windows, and the wise son knows a window when he sees it. Sleeping is not a sin in this proverb; sleeping in harvest is the folly, effort withheld now, when now is the only time the field is offering anything. The "son" language ties the pair back to 10:1 and keeps it in the family: his diligence or shame lands on the household, not just himself.
Related: Proverbs 6:6–8 · Proverbs 20:4
New King James Version®, Copyright © 1982, Thomas Nelson. All rights reserved. Full copyright information. Scripture provided by API.Bible.
Go Deeper
If this verse has been used to put weight on you that it was never carrying, ask about it directly.