The purpose of using the medal in any of the above ways is to call down God's blessing and protection upon us, wherever we are, and upon our homes and possessions, especially through the intercession of St. Benedict. By the conscious and devout use of the medal, it becomes, as it were, a constant silent prayer and reminder to us of our dignity as followers of Christ.

The medal is a prayer of exorcism against Satan, a prayer for strength in time of temptation, a prayer for peace among ourselves and among the nations of the world, a prayer that the Cross of Christ be our light and guide, a prayer of firm rejection of all that is evil, a prayer of petition that we may with Christian courage "walk in God's ways, with the Gospel as our guide," as St. Benedict urges us.
(excerpt from http://www.osb.org/gen/medal.html. For more information, please click on this link.)