aham atma gudakesha
aham adis ca madhyam ca
bhutanam anta eva ca

"I am the Supersoul, O Arjuna, seated in the hearts of all living entities. I am the beginning, the middle and the end of all beings."

Each line of the verse gives a meaning. He tells Arjuna that all the things he perceives are all His property. It is not like what we possess property. If we have money we can keep it in lockers or in our briefcase, remembering that money is physically different and separate form us. But the property of the Lord is not like that. They are always associated with Him as an integral part. All of them are His body. When atman resides in a body, it gets a name and is identified. Atman as such has no name but when it is in a body, the body gets a name and atman also is recognized with that name, as long as it is in that body. If we call a person, he turns. Though the name is for the body, without the command of atman, the body will not turn. In a similar way, the Lord is the atman in everything. He is residing in our atman as antharatman and is residing also in the body as atman. Thus all atman are the body of the Lord; also, all the materials are His body. Aham = I [ Sri Krishna] am, atma = the antharathma or inner soul, gudakesha = vanquisher of sleep [Arjuna]. Gudaka means sleep, isha means commander. Sarva bhuta = in every living beings, asaya =hearts, sthitha = established or dwelling. Our body obeys our commands,and so our body is our property. Like this, He is the inner atman in every atman or living beings and so all are His property. All are to obey His commands. This is called sareera-atma bhava or the relationship of He being soul and all His body. In the next line He says the cause-effect relationship. Mud is cause and pot is effect. Gold is cause and ornaments are effects. Similarly, the Lord is the Cause and all others are effects. Aham = I [Sri Krishna] am, adi = Cause for creation, madhyam ca = also the sustainer or protector of all created, anta eva ca = even the end at the time of Pralayam , bhutanam = of all living beings. He is the Cause for creation, sustaining and destruction, of all. This is called karana-karya bhava or cause-effect relationship. He is the supporter. He is the Commander. He is the proprietor. He is the Leader. Nothing is not in His control or ownership. If we clearly understand this, then it would be easier to understand the list He is going to deliver from sloka 21 to sloka 39.