The concept of an angel assigned to guide and nurture each human being is a development of Catholic doctrine and piety based on Scripture but not directly drawn from it. Jesus’ words in Matthew 18:10 best support the belief: “See that you do not despise one of these little ones, for I say to you that their angels in heaven always look upon the face of my heavenly Father.”
Devotion to the angels began to develop with the birth of the monastic tradition. St. Benedict gave it impetus and Bernard of Clairvaux, the great 12th-century reformer, was such an eloquent spokesman for the guardian angels that angelic devotion assumed its current form in his day. read more…
Source: http://www.americancatholic.org/features/saints/saint.aspx?id=1156
