In plain words
When the mind stirs even a little, that is the round of birth and death. When it stands unmoving, that is liberation. This is settled. So the mind has to be made firm; therefore, wise one, look to it with the supreme understanding.
Word for word
When the mind moves even a little, there is samsara; when it stands unmoving, liberation. This is established. Therefore, discerning one, make the mind steady through supreme understanding.