These verses supplement Ecclesiastes 8:15 with the reflection that the man who goes beyond that limited sphere within which he can labor and be contented, and investigates the whole work of God, will find that his finite intelligence cannot grasp it.
Business - Or, “travail” Ecclesiastes 1:13; Ecclesiastes 3:10. The sleeplessness noted probably refers to the writer himself.
16 When I applied mine heart to know wisdom, and to see the business that is done upon the earth: (for also there is that neither day nor night seeth sleep with his eyes:)
17 Then I beheld all the work of God, that a man cannot find out the work that is done under the sun: because though a man labour to seek it out, yet he shall not find it; yea further; though a wise man think to know it, yet shall he not be able to find it.