Angels are servants and messengers from God. "Angel" in Greek means messenger. In unseen ways the angels help us on our earthly pilgrimage by assisting us in work and study, helping us in temptation and protecting us from physical danger.
Each person on earth has a guardian angel who watches over him and helps him to attain his salvation. It has been a common theological opinion that this angelical guardianship begins at the moment of birth; prior to this, the child would be protected by the mother's guardian angel. But this is not certain, and since we now know that the soul is infused at the moment of conception, it may be that the angelic guardianship also begins at that moment.
In any case, this protection continues throughout our whole life and ceases only when our probation on earth ends, namely, at the moment of death. Our guardian angel accompanies our soul to purgatory or heaven, and becomes our coheir in the heavenly kingdom.
"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"
"Beside each believer stands an angel as protector and shepherd leading him to life"
Angel of God, my Guardian dear, to whom His love commits me here, ever this day (or night) be at my side, to light and guard, to rule and guide. Amen.