The path of the righteous is like the morning sun,
shining ever brighter till the full light of day.
But the way of the wicked is like deep darkness;
they do not know what makes them stumble.
The Holy Bible : Today’s New International Version. 2005 (Pr 4:18–19). Grand Rapids, MI: Zondervan.
The first and second line are an example of synthetic parallelism, where the second line builds upon and expands on the first line. The third and fourth lines work the same way, with the fourth line building upon and expanding upon the third line. The first and second lines are in antithetical parallelism with the third and fourth line: that is, they are opposites. These four lines are brilliant examples of rather complex Hebrew parallelism.
And the structure of the passage serves the goal of the meaning: to contrast the outcomes of wisdom and folly.