If the iron be blunt - If the axe have lost its edge, and the owner do not sharpen it, he must apply the more strength to make it cut: but the wisdom that is profitable to direct will teach him, that he should whet his axe, and spare his strength. Thus, without wisdom and understanding we cannot go profitably through the meanest concerns in life.
The figures seem to be taken from the work of building up and pulling down houses. In their general application, they recommend the man who would act wisely to be cautious when taking any step in life which involves risk.
Ecclesiastes 10:8
Breaketh an hedge - Rather: “breaks through a wall.”
Serpent - The habit of snakes is to nestle in a chink of a wall, or among stones (compare Amos 5:19).
Ecclesiastes 10:9
Be endangered - Rather: “cut himself.”