C. F. Keil and Franz Delitzsch on Proverbs 16:17

Pro 16:17 17 The path of the righteous is the avoiding of evil,      And he preserveth his soul who giveth heed to his way.

The meaning of מסלּה, occurring only here in the Proverbs, is to be learned from Pro 15:19. The attribution denotes that wherein the way they take consists, or by which it is formed; it is one, a straight and an open way, i.e., unimpeded, leading them on, because they avoid the evil which entices them aside to the right and the left. Whoever then gives heed to his way, preserveth his soul (שׁמר נפשׁו, as Pro 13:3, on the contrary Pro 25:5, subj.), that it suffer not injury and fall under death, for סוּר מרע and סור ממוקשׁי מות, Pro 14:27, are essentially the same. Instead of this distich, the lxx has three distichs; the thoughts presented in the four superfluous lines are all already expressed in one distich. Ewald and Hitzig find in this addition of the lxx a component part of the original text.