John Donne’s Meditation XVII includes this well-known passage:
No man is an island, entire of itself; every man is a piece of the continent, a part of the main; if a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as if a manor of thy friend's or of thine own were; any man's death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bell tolls; it tolls for thee. 
Donne’s point is that each and every person is part of every other person. None of us belongs to ourselves. “When [the Church] baptizes a child, that action concerns me; for that child is thereby connected to that head which is my head too, and ingrafted into that body, whereof I am a member.” No person is from himself. We are all interconnected and dependent upon one another. We need many things. We need one another.
But God is different. God has no need. “God has all life, glory, goodness, blessedness, in and of himself; and is alone in and unto himself all-sufficient, not standing in need of any creatures which he has made, nor deriving any glory from them, but only manifesting his own glory in, by, unto, and upon them” (WCF 2.2). God is not needy. He does not need you. He does not need anything or anyone in this world. He doesn’t need this world. God is not dependent upon anyone or anything. Positively put, God possess fullness of life in and of himself. God not only possesses fullness of life, God is fullness of life. This is what we mean when we talk about God’s attribute of aseity.
Perhaps aseity is not a term with which you are familiar. You’re not alone. I examine candidates for ordination in our denomination, and frequently (sadly) these men are unfamiliar with the term. Aseity comes from the Latin a se meaning “from himself.” In reference to God it means that God is self-sufficient and self-existent.
The Bible begins with these words, “In the beginning God created…” (Gen. 1:1). Before there was anything that was created, there was God. The only thing that existed before creation was God. What was God doing before creation? Was he like my kids in the backseat of the van on a long car trip, “I’m boooorrrred”? Was God lonely? Did God create the world to fulfill some missing part of his being or purpose? Did God look at the work of creation and say, “You complete me”? The Bible clearly declares NO. God was not bored or lonely or unfulfilled or purposeless before the world had been created. We tend to think this way because, frankly, we’re narcissists. God was perfectly and fully satisfied and content and happy in himself. He did not create out of a need. There is nothing in him that must be fulfilled or satisfied. God is from himself.
What are the implications of God’s aseity for us? How does this become something more than just pious ivory tower theology talk? If God is self-existent, self-fulfilled, perfect, and absolute in and of himself, dependent upon no one and no thing, then all of creation is dependent upon God for any and all good. Those communicable attributes which we find to some degree reflected in our personal attributes are sourced in God. Anselm said that God “is the good without which there is no good.” He is the beauty without which there is no beauty. He is the wisdom without which there is no wisdom. He is the righteousness without which there is no righteousness. He is the source and the cause of everything that is good.
God’s aseity means that God is not dependent upon us. God is not like the idols of Isaiah 40 and 44. Those idols are shaped and fashioned by hands out of wood and metal. They have ears but do not hear. They have mouths but do not speak. They are weak and impotent. They can deliver no one. But Paul describes God as “The God who made the world and everything in it, being Lord of heaven and earth, does not live in temples made by man, nor is he served by human hands, as though he needed anything, since he himself gives to all mankind life and breath and everything” (Acts 17:24, 25). God “created all things, and by [his] will they existed or were created” (Rev 4:11).
God’s aseity means he is independent of his creation. He does not need us, but we need him. If God were not independent, then he would not be dependable to save us or worthy of our praise. If God were not independent, then he would be dependent upon some other thing, and that thing would, in fact, be God. A God who is not independent and a se would be a God in our world but not a God distinct from our world. That God would be “a piece of the continent, a part of the main.” But a God who is self-existent and self-fulfilled and perfect in himself is entire of himself. He is a God worthy of praise and able to save lost sinners like you and me.
 Donne, John. The Works of John Donne. Vol. 3, 574-5.
 Barrett, None Greater, 68.
 Barrett, 69.