bahirantaśca bhūtānāmacaraṁ carameva ca
sūkṣmatvāttadavijñeyaṁ dūrasthaṁ cāntike ca tat
He exists, within and without all beings, and constitutes the animate and also the inanimate creation. He is both near and far away. Because of His subtlety, He is incomprehensible.
In the twelfth verse, God has been called 'Jñeya' (can be experienced), but in this verse He has been called 'Avijñeya' (can't be known). It means that in spite of the fact that God is 'Jñeya' but He is not known like knowing the world. As the world is known through senses, mind and intellect, God in not known through senses, mind and intellect. Senses, mind and intellect are the evolutes of Prakṛiti. The evolutes of Prakṛiti cannot know even Prakṛiti completely, then how can they know God Who transcends Prakṛiti? One has to accept the existence of God; because the acceptance is done by the Self itself. The Self has its identity with God, therefore God is also attained by acceptance and not by thinking, reflection and description.
Gita Prabodhani by Swami Ramsukhdasji