The existence of angels is a dogma of our Catholic Faith, and is abundantly documented in Sacred Scriptures and Catholic Tradition.
An angel is a spiritual creature, superior to human beings, with a three-fold mission: to praise God, to act as His messengers, and to watch over mortals. "What is man, that thou art mindful of him? ... For thou hast made him a little lower than the angels, and hast crowned him with glory and honor" (Psalm 8:4-5).
The name "angel" is from the Greek "angelos" meaning "one who is sent" or "messenger". Though purely spiritual, they can show themselves to men in human form as in the story of Tobias.
Passages in Scripture point to the existence of an angel specifically assigned to each human being to help, guide and protect him or her through the journey of life: “Behold I will send my angel, who shall go before thee, and keep thee in thy journey, and bring thee into the place that I have prepared. Take notice of him, and hear his voice” (Exodus 23:20) And in the words of Our Lord Jesus Christ speaking of children: “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).
Guardian Angels are often visible to Catholic saints as in the life of St. Frances of Rome, St. Gemma Galgani and St. Pio of Pietrelcina. St. Gemma’s angel even delivered letters for her, and brought her coffee in bed when she was sick.
Like many other feasts, the feast of the Guardian Angels was celebrated on a local level before it was placed on the Roman calendar. Pope Clement X officially established the feast of the Guardian Angels for the Universal Church on October 2.