God shows His love to us in many ways, and one of the most comforting and constant expressions of this is that He entrusts each of us to a particular angel, who is our guide and our guardian. The Catechism of the Catholic Church teaches us that "the existence of the spiritual, non-corporeal beings that Sacred Scripture usually calls 'angels' is a truth of faith” (n. 328), and it goes on to say (n. 336) "Beside each believer stands an angel as protector and shepherd leading him to life." Our Lord Himself tells us, "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" (Matthew 18:10).
St. Bernard of Clairvaux, in writing to his spiritual sons (and equally applicable to all of us) says this:
“Be alert in your every action as one should be who is accompanied by angels in all your ways, for that mission has been enjoined upon them. In whatever lodging, in whatever nook or corner you may find yourself, cherish a reverence for your guardian angel. In his presence do not dare to do anything you would not do in mine. Or do you doubt his presence because you do not see him? Would it really help if you did hear him, or touch him, or smell him? Remember, there are realities whose existence has not been proven by mere sight.
Brethren, we will love God's angels with a most affectionate love; for they will be our heavenly co-heirs some day, these spirits who now are sent by the Father to be our protectors and our guides. With such bodyguards, what are we to fear? They can neither be subdued nor deceived; nor is there any possibility at all that they should go astray who are to guard us in all our ways. They are trustworthy, they are intelligent, they are strong — why, then, do we tremble? We need only to follow them, remain close to them, and we will dwell in the protection of the Most High God. So as often as you sense the approach of any grave temptation or some crushing sorrow hangs over you, invoke your protector, your leader, your helper in every situation. Call out to him and say: Lord, save us, we are perishing.”
O Everlasting God, who hast ordained and constituted the ministries of angels and men in a wonderful order: Mercifully grant that, as thy holy angels always serve and worship thee in heaven, so by thine appointment they may help and defend us on earth; through Jesus Christ thy Son our Lord, who liveth and reigneth with thee and the Holy Ghost ever, one God, world without. Amen.