We cannot express in a few words what this is. It is contained in the four Gospels. We can try to hint at it by saying that God is unity, and he who abides in unity abides in God, and God in him. We believe that God's whole creation with all its star-worlds and worlds of spirits shall become one. If we look at Jesus' life we can see by contrast that this unity does not yet exist in creation.
Sin is there.
Sin is separation from unity. Satan and his demons surround the earth like an atmosphere. Jesus speaks quite plainly of satanic power. He calls this devilish power Mammon. You cannot serve God and Mammon.