By Fr. Thomas G. Weinandy,
Like many people years ago, as a child, my brother and I, together with our dad, always prayed in our "night prayers" the traditional prayer to our guardian angels: "Angel of God, my guardian dear to whom God's love entrusts me here, ever this day (or night) be at my side, to light and guard, to rule and guide. Amen."
I still ask my guardian angel at night when I go to bed and, in the morning, when I get up, to watch over and protect me. Moreover, before writing, I always ask my guardian angel to give me clarity of thought and expression and to whisper the right words into my ears. Sometimes when I am struggling to find the right word, he places exactly the right word in my mind.
Prayers to one's guardian angel are Biblically based:
• God instructs Moses, as the Israelites set off for the Promised Land: "Behold I send you an angel before you, to guard you on the way and bring you to the place which I have prepared. Give heed to him and hearken to his voice." (Exodus 23:20-21).
• Psalm 91:11 affirms that one need not fear, "for he (God) will give his angels charge over you to guard you in all your ways."
• Jesus himself states that we should not despise the little ones, "for I tell you that in heaven their angels always behold the face of my Father who is in heaven." (Matthew 18:10)
• In the Acts of the Apostles, when Peter escapes from prison and knocks on the door where the faithful were gathered, his brethren wrongly think: "It is his angel!" (Acts 12:13-15)
Although most of us will never see our guardian angels, many saints have. Padre Pio frequently conversed with his guardian angel, who would defend him against demonic attacks. Gemma Galgani was in daily contact with her guardian angel, who taught, protected, and corrected her. Sr. Faustina Kowalska spoke of her guardian angel accompanying her on her journeys. She also saw him when she was immersed in prayer, often asking her to pray for the dying.

The point of the above examples is not to say that one has to be a "saint" to speak with or behold one's guardian angel. Rather, it is to illustrate that we, too, can converse with and be assured of our guardian angel's protecting and guiding presence.
Moreover, we should dispel the romantic and "cute" notion that guardian angels are only relevant for vulnerable children. Adults are in as much need of their guardian angels – maybe even more so, for their temptations and affairs are often of a more serious nature.
Our guardian angels are therefore present to strengthen, to encourage, and to guide us in living out our respective vocations, whether single, married, religious, or priestly. To dismiss them as only suited for what is childish is to place ourselves in harm's way.
The question has been asked: After death, do our guardian angels cease to be with us once we enter into Heaven? Obviously, we no longer need to be guarded. Do they, then, get recycled to someone newly conceived?
According to Catholic tradition, our guardian angels even remain with us in Heaven and together we give praise and glory to the most holy Trinity – to our heavenly Father who is the ultimate source of life, to the risen Jesus, the Father's incarnate Son, who is our loving Savior and Lord, and to the Holy Spirit who cleanses us of sin and makes us holy.
With all of our brothers and sisters in Christ, along with our respective guardian angels, we will sing forever a glorious hymn of praise and thanksgiving.
Here, we perceive the confluence of the earthly and the heavenly liturgy. At the conclusion of the Preface at Mass the following, or something similar, is said: "And so, with the Angels and all of the Saints we declare your (the Father's) glory, as with one voice we acclaim: Holy, Holy, Holy, Lord God of hosts. Heaven and earth are full of your glory."
With one voice, our earthly human voices, the heavenly voices of the saints, and the host of angelic voices, we all together declare that both Heaven and earth are filled...

Guardian Angels: Not Just Kid-Stuff