How did feudalism provide for the security of the people of medieval Europe?

It was a mutual relationship where the serf/peasant/farmer would provide goods and food, as well as other services for his feudal lord, while the feudal lord, on the other hand, would provide him with security against foreign attackers, or just other potential enemies that might arise.

This is how the feudal seystem provided security both ways from peasants to lords and the other way around.