Fear of Punishment

A person should serves Hashem mainly from fear. Even Tzadikim mostly serve Hashem out of fear and those that constantly serve Hashem from love are few. Fear of punishment is the main element of fear. There is a higher level of fear called Fear of His Awesomeness, that is to fear Hashem due to His tremendous greatness and power. Since not everyone merits this, the main service of Hashem for most people has to be based on fear of being punished for doing wrong. Every person is born with evil and it is their natural tendency to be pulled after this evil, that is after the desires and lusts of the physical world. It is only because fear of punishment that a person breaks his lusts and desires and starts entering into the service of Hashem.

(Sichos Haran 5)