Bhagavad Gita: Chapter 13, Verse 16

बहिरन्तश्च भूतानामचरं चरमेव च |
सूक्ष्मत्वात्तदविज्ञेयं दूरस्थं चान्तिके च तत् || 16||

bahir antaśh cha bhūtānām acharaṁ charam eva cha
sūkṣhmatvāt tad avijñeyaṁ dūra-sthaṁ chāntike cha tat

bahiḥ—outside; antaḥ—inside; cha—and; bhūtānām—all living beings; acharam—not moving; charam—moving; eva—indeed; cha—and; sūkṣhmatvāt—due to subtlety; tat—he; avijñeyam—incomprehensible; dūra-stham—very far away; cha—and; antike—very near; cha—also; tat—He

bahir antash cha bhutanam acharam charam eva cha
sukshmatvat tad avijneyam dura-stham chantike cha tat

Translation

BG 13.16: He exists outside and inside all living beings, those that are moving and not moving. He is subtle, and hence, He is incomprehensible. He is very far, but He is also very near.

Commentary

There is a Vedic Mantra that describes God in practically the same manner as Shree Krishna has described here:

tad ejati tan naijati taddūre tadvantike

tad antar asya sarvasya tadusarvasyāsya bāhyataḥ   (Īśhopaniṣhad mantra 5)  

“The Supreme Brahman does not walk, and yet He walks; He is far, but He is also near.  He exists inside everything, but He is also outside everything.” 

Previously in verse 13.3, Shree Krishna said that to know God is true knowledge.   However, here He states that the Supreme Entity is incomprehensible.  This again seems to be a contradiction, but what He means is that God is not knowable by the senses, mind, and intellect.  The intellect is made from the material energy, so it cannot reach God who is Divine.  However, if God Himself bestows His grace upon someone, that fortunate soul can come to know Him.