According to Isaiah, this verse is like telling a story about a farmer who carefully puts each different seed in the right spot in his field, just like God has a special plan for everything he does. It's a way of reminding us that God knows what he's doing, and everything has its own special place.
Isaiah 28:25: When he hath made plain the face thereof, doth he not cast abroad the fitches, and scatter the cummin, and cast in the principal wheat and the appointed barley and the rie in their place? [the principal...: or, the wheat in the principal place, and barley in the appointed place] [rie: or, spelt] [place: Heb. border?]
While Isaiah 28:25 describes a process of thorough preparation and orderliness, Proverbs 21:5 emphasizes diligent planning but warns that hasty actions, in contrast, lead to poverty, suggesting that mere order does not guarantee success without careful planning and timing.
Proverbs 21:5: The thoughts of the diligent [tend] only to plenteousness; but of every one [that is] hasty only to want.