Purport

As described in earlier Shlokas, getting perfection in Meditation is a delicate and long process. Achieving perfection in Yoga becomes more difficult also due to the volatile nature of the mind. It is kind of impossible to keep the mind free of thought even for a short period of time. This is hence quite obvious that a Yogi practicing meditation may find his mind fickle and wonder in different thoughts.

In the above shloka, Bhagvan Shri Krishna warns for the same. Whenever mind wonders in thoughts or desires, the yogi should bring it back then and there to focus on self alone, think of Parmatma Bhagvan Shri Krishna only. By constantly practicing this way, yogi certainly achieves perfection.