SB 10.14.6

tathāpi bhūman mahimāguṇasya te
 viboddhum arhaty amalāntar-ātmabhiḥ
avikriyāt svānubhavād arūpato
 hy ananya-bodhyātmatayā na cānyathā
Word for word: 
tathā api — nevertheless; bhūman — O limitless one; mahimā — the potency; aguṇasya — of Him who has no material qualities; te — of You; viboddhum — to understand; arhati — one is able; amala — spotless; antaḥ-ātmabhiḥ — with mind and senses; avikriyāt — not based on material differentiations; sva-anubhavāt — by perception of the Supreme Soul; arūpataḥ — without attachment to material forms; hi — indeed; ananya-bodhya-ātmatayā — as self-manifested, without the help of any other illuminating agent; na — not; ca — and; anyathā — otherwise.
Translation: 
Nondevotees, however, cannot realize You in Your full personal feature. Nevertheless, it may be possible for them to realize Your expansion as the impersonal Supreme by cultivating direct perception of the Self within the heart. But they can do this only by purifying their mind and senses of all conceptions of material distinctions and all attachment to material sense objects. Only in this way will Your impersonal feature manifest itself to them.
Purport: 

It is difficult for conditioned souls to understand all the transcendental features of the Supreme Lord. As confirmed in the First Canto of Śrīmad-Bhāgavatam (1.2.11): brahmeti paramātmeti bhagavān iti śabdyate. The transcendental existence of God is understood progressively as the impersonal effulgence, the localized Supersoul in one’s heart, and finally the Supreme Personality of Godhead existing in His eternal abode. Lord Kṛṣṇa’s transcendental existence is beyond the qualities of material nature. Thus here the Lord is referred to as aguṇasya, without material qualities.

Even by practicing yoga or engaging in advanced philosophical speculation, one will find it very difficult to understand clearly the transcendental existence beyond the modes of material nature. And these processes are virtually useless for understanding the Lord’s own unlimited transcendental qualities, which are far beyond the impersonal conception of spiritual existence. Only by the mercy of the pure devotees of the Lord or by associating with the Lord Himself can one begin the process of realizing the personal feature of God — a process that culminates in pure Kṛṣṇa consciousness, the final and supreme perfection of knowledge.