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:)
When I applied mine heart to know wisdom ... - When I applied myself to observe man's toils after happiness (some of them so incessant as not to allow sufficient time for "sleep;" cf. Genesis 31:40; Proverbs 6:4; Psalms 132:4), then (Ecclesiastes 8:17, the apodosis) I saw that "man" cannot find out (the reason of) God's inscrutable dealings with the "just" and with the "wicked" here (Ecclesiastes 8:14; Ecclesiastes 3:11; Job 5:9; Romans 11:33); his duty is to acquiesce in them as good, because they are God's, though he sees not all the reasons for them (Psalms 73:16). It is enough to know 'the righteous are in God's hand' (Ecclesiastes 9:1).
Though a wise (man) think to know (it) ... Compare "neither make thyself overwise" (Ecclesiastes 7:16), speculating above what is written. God has His wise and just reasons for all that is done or permitted here, but they are secret to us. 'If the works of Solomon so struck with admiration the queen of Sheba that "there was no more spirit in her" (1 Kings 10:5), much more the works of God, which exceed all our, intelligence, ought to fill us with admiration' (Cartwright).