To possess a key is to possess the pivotal knowledge of some eternal principle that grants access to higher levels of spiritual ability and power. A very small key can open a very large door. But take away the key and the door may as well be a wall.
Islam looks at every individual as a human being first, who needs to satisfy all of their basic needs completely. Then it looks to them in their capacity as a particular individual, to enable them to satisfy their luxuries as much as possible.