Final answer:
The manager should instruct Marvin on the essential checks for food quality and safety when receiving a delivery, including inspecting the temperature, damage, and correctness of the items delivered.
Step-by-step explanation:
The most important thing that the manager must communicate to Marvin to keep food safe is the importance of checking the quality and safety of the food upon delivery. This includes ensuring that the food is at the correct temperature, checking for any signs of damage or contamination, and confirming that the delivery contains the correct items and quantities. By emphasizing to Marvin the essential checks for food quality and safety, the manager ensures that the task of receiving a delivery is executed with the utmost importance placed on food safety standards.