Here is an example to help you understand the efficacy of the Rosary. You remember the story of David who vanquished Goliath. What steps did the young Israelite take to overthrow the giant? He struck him in the middle of the forehead with a pebble from his sling. If we regard the Philistine as representing evil and all its powers: heresy, impurity, pride, we can consider the little stones from the sling capable of overthrowing the enemy as symbolizing the Aves of the Rosary.