This is a quotation from Śrīmad-Bhāgavatam (1.2.11). For an explanation, see also Ādi-līlā, Chapter Two, verse 11.

Those who are interested in the impersonal Brahman effulgence which is not different from the Supreme Personality of Godhead, can attain that goal by speculative knowledge. Those who are interested in practicing mystic yoga can attain the localized aspect of Paramātmā. As stated in Bhagavad-gītā, īśvaraḥ sarva-bhūtānāṁ hṛd-deśe 'rjuna tiṣṭhati: the Supreme Personality of Godhead is situated within the heart as Paramātmā. He witnesses the activities of the living entities and gives them permission to act.