Often renunciants are more inclined toward
aṣhṭāṅg-yog
or
haṭha-yog
along with their practice of asceticism.  Their extreme detachment makes them disinterested in the path of devotion, which requires meditation on the Names, Forms, Pastimes, and Abodes of God.  Shree Krishna here describes the path that the ascetics take.
He says that such ascetics shut out thoughts of sense objects by controlling their sight and breath.  They focus their gaze between their eyebrows.  If the eyes are fully closed, sleep may overtake one; and if they are wide open, they may get distracted by the objects around them.  In order to avoid both these defects, the ascetics concentrate their gaze, with eyes half-open, between the eyebrows or the tip of the nose.  They also harmonize the
prāṇ
(outgoing breath) with the
apān
(incoming breath), until both become suspended in yogic trance.  This yogic process enables the controlling of the senses, mind, and intellect.  Such persons make liberation from the material energy as their only goal.
Such ascetic practices lead to
ātma jñāna
(knowledge of the self), not to
brahma jñāna
(knowledge of God).  Hence, the ascetic path must also be consummated through devotion to God, as stated in the next verse.