Excerpt from: “The Spiritual Life. A Treatise on Ascetical and Mystical Theology”, [pgs. 97-98] by The Very Reverend Adolphe Tanquerey, S.S., D.D.
“Some among the Angels are commissioned with the care of individual souls: these are the Guardian Angels. This is the traditional doctrine of the Fathers, based upon scriptural texts and supported by solid reasons. It has been confirmed by the Church in the institution of a feast in honor of the Guardian Angels. The reasons that support this doctrine flow from our relationship to God, for we are His children, members of Jesus Christ and temples of the Holy Ghost. “Because we are His children,” says Father Olier, “He appoints to us as tutors the princes of His realm, who hold it an honor to have us in their charge. Because we are His members, He wills that those very spirits that minister unto Him be also at our side to render us their services. Because we are His temples in which He Himself dwells, He wills that Angels hover about us as they do about our churches, so that bowed down in worship before Him they may offer a perpetual homage to His glory, supplying for our neglect and making reparation for our irreverence.” Father Olier goes on to say that God wishes to unite intimately through the agency of His Angels the Church Triumphant and the Church Militant: “He sends this mysterious host of Angels in order that they may by uniting themselves to us and binding us to themselves form one body of the Church of heaven and the Church of earth.”
Note: The “Father Olier” referred to by Fr. Tanquerey is Father J.J. Olier (1608-1657), founder of the Society of St. Sulpice.