Jamieson, Fausset & Brown

Wherefore--seeing that ye need to walk so circumspectly, choosing and using the right opportunity of good. unwise--a different Greek word from that in Eph 5:15. Translate, "foolish," or "senseless." understanding--not merely knowing as a matter of fact (Luk 12:47), but knowing with understanding. the will of the Lord--as to how each opportunity is to be used. The Lord's will, ultimately, is our "sanctification" (Th1 4:3); and that "in every thing," meantime, we should "give thanks" (Th1 5:18; compare above, Eph 5:10).