Chapter One - Mishna 3 (2)
And let the fear of Heaven be upon you
Antignos goes on to say, "Even though you serve Hashem because you love Him, you must also serve Him with fear." If a person loves Hashem, he wants to do as much as possible. He keeps all of the mitzvos of the Torah. But fear of Hashem protects a person from doing those things the Torah tells him not to do. This boy is trying to fight the Satan. If we serve Hashem with both love and fear, we can serve Him completely and push the Satan out of the picture.