“Wherefore be ye not unwise, but understanding what the will of the Lord is.”
No Christian should be unwise or a fool. It is most displeasing to God that Christians make unwise choices and act foolishly. This advice was already given in verse 15 – “See then that ye walk circumspectly, not as fools, but as wise”.
The next advice in our text is how to avoid being fools, and thus be wise. The advice is that we must understand what the will of the Lord is. If we think, speak or act apart from God’s will, we will be foolish in our conduct.
But how can we know God’s will? It is not through dreams and visions that the Lord makes known His will to us. The help to know God’s will comes through God’s Word. The Bible is given to us, that we may know God’s will about our life. If we study the Bible and apply (i.e. believe and obey) its truths in our thinking, speech and actions, we will know how to avoid foolishness and conduct ourselves wisely.
So, every Christian “no longer should live the rest of his time in the flesh to the lusts of men, but to the will of God.”