Carl Friedrich Keil and Franz Delitzsch Old Testament Commentary

5 The righteousness of the blameless smootheth his way, And by his own wickedness doth the wicked fall. With the תּמים (cf. Pro 1:12), formed after the passive, more than with תּם, is connected the idea of the perfected, but more in the negative sense of moral spotlessness than of moral perfection. The rectitude of a man who seeks to keep his conscience and his character pure, maketh smooth (ישּׁר, as Pro 3:6, not of the straightness of the line, but of the surface, evenness) his life's path, so that he can pursue his aim without stumbling and hindrance, and swerving from the direct way; while, on the contrary, the godless comes to ruin by his godlessness - that by which he seeks to forward his interests, and to make a way for himself, becomes his destruction.