Because the sentence against an evil deed is not executed speedily, the heart of the children of man is fully set to do evil.
Solomon, in the beginning of the chapter, had warned us against having any thing to do with seditious subjects; here, in these verses, he encourages us, in reference to the mischief of tyrannical and oppressive rulers, such as he had complained of before, Ecc 3:16; Ecc 4:1. 1. He had observed many such rulers, Ecc 8:9.
Commenting on Ecclesiastes 8:9-13
Because sentence against an evil work is not executed speedily,.... Any evil work done by magistrates, or others, against which the wrath of God is revealed from heaven, and is threatened with his vengeance; the decree is gone forth, the sentence is passed, God is determined upon punishment; but there is a delay of it, he exercises patience and longsuffering to answer some end of...
The reason why the wicked persevere in sin: God's delay in judgment (Mat 24:48-51; Pe2 3:8-9). "They see not the smoke of the pit, therefore they dread not the fire" [SOUTH], (Psa 55:19). Joab's escape from the punishment of his murder of Abner, so far from "leading him to repentance," as it ought (Rom 2:4), led him to the additional murder of Amasa.