Gradually and steadily with close attention, withdraw yourself by employing diligently the intelligence controlled by the will. Once the mind becomes self-ward and finally self-settled, do not think at all. (All thinking and willing must come to a stop.)
Explanation of verses 6.24 and 6.25 –
Krishna spoke about the first phase of meditation, in which āsana (seat), pose and the limbs play a part. But all these are intended to enable one to reach the mind-arena and learn to steer it safely to the goal.
In other words, accessing the mind and leading it well is the first aim. Once the entry into the mind is safely had, and the seeker understands the mind-intellect complexity, the entire effort becomes inner alone, involving nothing else.
One may sit anywhere, in any manner. He can still access the mind and proceed therefrom confidently. Krishna thus explains the second level of meditation, which takes the yogi straight to his desired goal.
Get into the mind, leave all kinds of desire resulting from imaginations and assessments. Disconnect the mind from sensory entanglement, by employing the discreet intelligence. Understand well that the intelligence alone has the power to act on the mind.
Have the mind, given generally to issue forth, recede and recede applying the power of discrimination. The mind will yield. The goal being the inmost Self, the mind need not go outward. It should instead be able to turn inward, delve within and dissolve without any hindrance at all.
In other words, it should not think at all, or think, yes, but nothing. Even the thought of Self becomes redundant. If one is the Self, then why say at all he is.
Whether one claims and says or not, that one is the Self is a fact that endures ever by itself. As it is, the Self was and will also be ever, unchanged, unaffected, self-glorious and blissful to the core. This confirmation, assurance, rules out all need for thinking and reflection. What a great release, poise!