Adam Clarke on Psalms 119:9

A young man cleanse his way - ארח orach, which we translate way here, signifies a track, a rut, such as is made by the wheel of a cart or chariot. A young sinner has no broad beaten path; he has his private ways of offense, his secret pollutions: and how shall he be cleansed from these? how can he be saved from what will destroy mind, body, and soul? Let him hear what follows; the description is from God.

1. He is to consider that his way is impure; and how abominable this must make him appear in the sight of God.

2. He must examine it according to God's word, and carefully hear what God has said concerning him and it.

3. He must take heed to it, לשמר lishmor, to keep guard, and preserve his way - his general course of life, from all defilement.