It is written in the midrash on the matter of livelihood: "It is difficult to make a living from redemption, that redemption is by means of a messenger and livelihood by God."
The key symbolizes the work that a person does on his part: "Develop a hole for me like the needle of a needle, and I will open the door to you as a spoon." God gives food to every creation (Pesachim 118a), as it is said: "Open your hand and give every living thing a will."