According to Medieval Angelology, there are nine Choir of Angels or celestial orders: Seraphim, Cherubim, Thrones, Dominions, Virtues, Powers, Principalities, Archangels and Angels. Each order of angels is given distinctive gifts from God. The gifts complement each other. Even though each Angel Choir is unequal in power, intelligence, and other gifts, they are equally loved by God.
The seraphim are the highest order. They are the angels who are attendants or guardians before God's throne. They praise God, singing, "Holy, holy, holy is the Lord of hosts; the whole earth is full of his glory" (Isaiah 6:3). One of them touched Isaiah's lips with a live coal from the altar, cleansing him from sin. Seraphim have six wings: two cover their faces, two cover their feet, and two are for flying.
Cherubim rank after the seraphim. They are manlike in appearance and double-winged and were guardians of God's glory. In the New Testament, they are alluded to as celestial attendants in the Apocalypse (Rv 4-6). Catholic tradition describes them as angels who have an intimate knowledge of God and continually praise Him.
Thrones are the Angels of pure Humility, Peace and Submisssion. They reside in the area of the cosmos where material form begins to take shape. The lower Choir of Angels need the Thrones to access God (Col 1:16).
Dominions are Angels of Leadership. They regulate the duties of the lower angels, making known the commands of God (Eph 1:21; Col 1:16). They also preside over nations.
Virtues are known as the Spirits of Motion and control the elements. They are sometimes referred to as "the shining ones." They govern all nature. They have control over seasons, stars, moon; even the sun is subject to their command. They are also in charge of miracles and provide courage, grace, and valor.
Powers are Warrior Angels against evil defending the cosmos and humans. They are known as potentates. They fight against evil spirits who attempt to wreak chaos through human beings (Rom 8:38; 1 Cor 15:24; Eph 1:21; 1 Pt 3:22; 2 Thes 1:7). They work diligently to oversee the distribution of power among humankind, hence their name.
Principalities refers to one type of spiritual being whose duty is to carry out the orders given to them by the Dominions and grant blessings to the material world. They oversee groups of people. As beings related to the world of the ideas, they inspire living things to many branches of knowledge such art and/or science.
Archangels are generally taken to mean "chief or leading angel" ( Jude 9; 1 Thes 4:16). They are the most frequently mentioned throughout the Bible. The Archangels have a unique role as God's messenger to the people at critical times in history and salvation (Tb 12:6, 15; Jn 5:4; Rv 12:7-9) as in The Annunciation and Apocalypse. St. Gregory says that the Archangels “strengthen people in the holy faith, enlightening their minds with the light of knowledge of the holy Gospel and revealing the mysteries of devout faith.” A feast day celebrating the Archangels Michael, Gabriel and Raphael is celebrated throughout the Church on September 29th.
Angels are closest to the material world and human beings. They deliver the prayers to God and God's answers and other messages to humans. Angels have the capacity to access any and all other Angels at any time. They are the most caring and social to assist those who ask for help. This order includes guardian angels of mankind.
"One of the ancient Fathers, whom we know today by the name St. Denis the Areopagite, explained that the hierarchy of angels in heaven reflects the hierarchy of the Church on earth. Hierarchy means 'sacred order' or 'sacred rule.' And God established this order, top to bottom, for the sake of service. Those who are 'highest' in rank—that is, those who have received the greatest spiritual gifts—must serve all those who are 'lower' in rank and bring them to greater knowledge of God. That is why, in the earthly Church, the pope is called 'servant of the servants of God.' He must serve you and me, and so must the most sublime among the angels" (4-Chapter 6 "A Gathering of Angels").
That is why Jesus came to serve, not to be served. He taught us that our job here on earth is to serve others. God makes all creatures to serve one another in love. Each angel and each human is created by God for the purpose of loving service. Just like the angels serve us, we must serve those who have less than us. The more we are given, the more He expects from us. If we are blessed with talents, we must put them to use for the service of others. If we are blessed with time, we must not waste it. We must ask God what He wants us to do with it and place our time at His service. If we are blessed with treasures, we must help the poor and those in need. And we will be surrounded by a choir of angels singing and praising as we join with them in angelic service.
The higher the angels are in the angelic hierarchy, the more God expects from them. The higher we are in the earthly hierarchy, the more God expects from us.
Sources:
1-The Catholic Edition of the Revised Standard Version of the Bible
2-Catechism of the Catholic Church (CCC)
3-"Entertaining Angels" by Mike Aquilina (Catholic Scripture Study International 2013)
4-"Angels and Saints" by Scott Hahn 2014
5-"City of God" by St. Augustine 426 AD