The following comes from Fr. George W. Rutler:
The Feast of the Archangels, Michael, Gabriel and Raphael on September 29, is quickly followed by the Feast of the Guardian Angels on October 2. Here we get into a deep science: not the natural science which increasingly is opening up the wonders of the physical universe, but rather the higher science of perfect spirits and incalculable intelligences, whose lowest "choirs" are the angels and archangels. Unlike natural science, this knowledge comes not from observation but from revelation. We use reason to acknowledge that there are wonders beyond our ability to reason, and that includes angels who have no need of reason because they are pure intellects.
Angels are creatures, but existed before the first man (Colossians 1:15-16). They are subject to Christ (1 Peter 3:21-22). They enjoy the constant presence of God (Luke 1:18-19). They are numerous beyond human calculation, and so they are described as thousands upon thousands, or myriads, since Hebrew has no word for “millions." (Hebrews 12:22-23). They know God's will but do not know all its details (Matthew 24:35-36). Angels are multi-lingual (1 Corinthians 4:9) and patrol the earth (Zechariah 1:10-11). Although Christ is divine, he can appear as an angel (Hosea 12:4-5). Angels can appear as winds and fire (Hebrews 1:7) and they rejoice when we go to Confession (Luke 15:9-20). Scripture never says that they have halos, and only seraphim and cherubim are described as having wings, so we would probably not recognize an angel if we saw one. They are astonishingly strong, so that one was able to slay 185,000 Assyrians. They want to comfort us (Matthew 28:1-7) and do not want us to give them the worship which is due to God alone (Colossians 2:18-19). Jesus had power to invoke 72,000 of them (twelve legions) had he wanted to avoid crucifixion, but he did not (Matthew 26:52-53). At the end of the created universe they will accompany Jesus in the Final Judgment (Matthew 25:31).
As angels have no bodies, they have no size, and so they care for everyone equally, regardless of size or age or worldly importance. Jesus said that the littlest human body has a guardian angel in heaven (Matthew 18:10). In each of us the guardian angels see their Lord and our Lord. So Pope Francis said on September 20: "Every child that isn't born, but is unjustly condemned to be aborted, has the face of Jesus Christ."
St. Pius of Pietrelcina (Padre Pio) wrote to a young girl: "Never say you are alone in sustaining the battle against your enemies. Never say you have nobody to whom you can open up and confide. You would do this heavenly messenger a grave wrong."