"For he hath given his angels charge over thee, to keep thee in all thy ways.” - Psalm 90:11
The truth that each and every human soul has a Guardian Angel who protects us from both spiritual and physical evil has been shown throughout the Old Testament, and is made very clear in the New.
It is written that the Lord Jesus was strengthened by an angel in the Garden of Gethsemane, and that an angel delivered St. Peter from prison in the Acts of the Apostles.
But Jesus makes the existence and function of guardian angels explicit when he says, "See that you despise not one of these little ones: for I say to you, that their angels in heaven always see the face of my Father who is in heaven." (Matthew 18:10).
In saying this Jesus points out that all people, even little children, have a guardian angel, and that the angels are always in Heaven, always looking at the face of God throughout their mission on earth, which is to guide and protect us throughout our pilgrimage to the house of our Father. As St. Paul says, "Are they not all ministering spirits, sent to minister for them, who shall receive the inheritance of salvation?" (Hebrews 1:14).
However, they guide us to Heaven only if we desire it. St. Thomas Aquinas wrote that angels cannot act directly upon our will or intellect, although they can do so on our senses and imaginations – thus encouraging us to make the right decisions. In Heaven our guardian angels, though no longer needing to guide us to salvation, will continually enlighten us.
Prayer to the guardian angels is encouraged, and the habit of remembering their presence and support leads to frienship with them. The prayer to the guardian angels has been present in the Church since at least the beginning of the 12th century:
Angel of God,
my Guardian dear,
to whom His love
commits me here,
ever this day
be at my side,
to light and guard,
to rule and guide.
“Let us affectionately love His angels as counselors and defenders appointed by the Father and placed over us. They are faithful; they are prudent; they are powerful; Let us only follow them, let us remain close to them, and in the protection of the God of heaven let us abide.” St. Bernard of Clairvaux