Shrimad Bhagavad Gita As It Is -Shri Shrimad A.C Bhaktivedanta Swami Prabhupada
The Opulence of the Absolute
Chapter 10: Verse-15
ssvayam evätmanätmänam vettha tavm purusottama
Indeed, You alone know Yourself by Your own internal potency, O Supreme Person, origin of all, Lord of all beings, God of gods, Lord of the universe!
The Supreme Lord, Krsna, can be known by persons who are in a relationship with Him through the discharge of devotional service, like Arjuna and his followers. Persons of demonic or atheistic mentality cannot know Krsna. Mental speculation that leads one away from the Supreme Lord is a serious sin, and one who does not know krsna should not try to comment on Bhagavad-gita. Bhagavad-gita is the statement of Krsna, and since it is the science of Krsna, it should be understood from krsna as Arjuna understood it. It should not be received from atheistic persons. As stated in 
vadanti tat tattva-vidas
The Supreme Truth is realized in three aspects: as impersonal Brahman, localized Paramätmä and at last as the Supreme Personality of Godhead. So at the last stage of understanding the Absolute Truth, one comes to the Supreme Personality of Godhead. A common man or even a liberated man who has realized impersonal Brahman or localized Paramätmä may not understand God’s personality. Such men, therefore, may endeavor to understand the Supreme Person from the verses of Bhagavad-gita, which are being spoken by this person, Krsna. Sometimes the impersonalists accept krsna as Bhagavän, or they accept His authority. Yet many liberated persons cannot understand Krsna as Purusottama, the Supreme Person. Therefore Arjuna addresses Him as Purusottama. Yet one still may not understand that krsna is the father of all living entities. Therefore Arjuna addresses Him as Bhüta-bhävana. And if one comes to know Him as the father of all the living entities, still one may not know Him as the supreme controller; therefore He is addressed here as Bhütesa, the supreme controller of everyone. And even if one knows krsna as the supreme controller of all living entities, still one may not know that He is the origin of all the demigods; therefore He is addressed herein as Devadeva, the worshipful God of all demigods. And even if one knows Him as the worshipful God of all demigods, one may not know that He is the supreme proprietor of everything; therefore He is addressed as Jagatpati. Thus the truth about krsna is established in this verse by the realization of Arjuna, and we should follow in the footsteps of Arjuna to understand krsna as He is.
- svayam=personally; eva=certainly; ätmanä=by Yourself; ätmänam=Yourself; vettha=know; tvam=You; purusa-uttama=O greatest of all persons; bhüta-bhävana=O origin of everything; bhüta-isa=O Lord of everything; deva-deva=O Lord of all demigods; jagat-pate=O Lord of the entire universe.
- Srimad-Bhägavatam 1.2.11