Technically, it's a visible depiction of an otherwise intangible characteristic: glory. In biblical stories, glory describes the "shine" of God, an emanation of light so powerful, it "afflicts" Moses, who's the one human being routinely standing close to God in the Old Testament. When Moses enters the Tent of the Presence, he comes out with an unbearable brightness in his face that requires him to veil himself. Either Moses is protecting the vestige of God's glory from being viewed by profane onlookers, or protecting the unprepared onlooker from a potentially dangerous contact with divinity's afterglow. As we know from other stories, unworthy contact with holy things can kill you. The tribe of Levi was dedicated to God as the only Israelites allowed to touch, tend, or transport utensils and objects used in ritual sacrifices for this reason. They made a living out of keeping themselves pure enough to perform their duties.

The Greeks also imagined sunbursts emanating from Helios, their sun god. Pharaohs of Egypt wear a crown of light in some depictions. It makes sense that Christians would employ the halo when portraying Christ, later extending the usage to angels and finally to saints. Jesus and Mary alone are honored with full body haloes, called aureoles—the most familiar of which surrounds the image of Our Lady of Guadalupe.

Most saints are portrayed with round haloes in the West, which can be thin circlets of gold or full discs of yellow. The circle is a perfect form, which hints at heavenly perfection. Some artistic renderings utilized a square halo when depicting a still living person who is revered: the square is an earthly, less perfect geometric form recalling the four elements, winds, or directions. A triangular halo is reserved for the less common depiction of God the Father, to recall the Triune nature of the divine. Very occasionally, Jesus will wear the triangular halo for the same reason. Jesus is the only icon who is permitted to be defined by the cruciform halo.

Sometimes anthropomorphic images of the Virtues—theological virtues like Faith, Hope, and Love, or the cardinal virtues Justice, Prudence, Fortitude and Temperance—will wear hexagonal haloes, to remind us they are attributes of God. So altogether, we conclude that the "shine" on a person or thing speaks to us of their nearness to God or their out-and-out resemblance to the divine. We should all be working on our shine!

Scriptures: Exodus 33:7-23; 34:27-35; Numbers 1:49-54; 1 Samuel chs. 4—6; 2    Samuel 6:1-19; 1 Kings 8:10-11; 1 Chronicles 23:25-32

Books: The Square Halo and Other Mysteries of Western Art - Sally Fisher (New York: Harry N. Abrahms, Inc., 1995).

Saints and the Symbols: Recognizing Saints in Art and in Popular Images -Fernando and Giolia Lanzi (Collegeville, MN: Liturgical Press, 2004).

Since some Catholics in their spiritual practice have little truck with saints or Marian devotion, it's more accurate to say that Catholic tradition holds Mary and the saints in high esteem. To answer this inquiry thoughtfully requires the introduction of key terms. The first is hyperdulia: it means "more than service," and it's the special honor Roman Catholic tradition renders to Mary as the Virgin Mother of Jesus and therefore Mother of God (theotokos in Greek).

This title, by the way, is a sensitive spot in historical relations with the Orthodox tradition, which prefers to call Mary the Mother of Christ (christotokos)—a distinction dear to theologians. That God/Christ has a mother thanks to the incarnation of Jesus is, by any measure, a remarkable consideration. Once you ponder that, you begin to appreciate what it means for a woman to collaborate with God in the world's salvation, to carry divinity within her body, or to raise God's son as her own. You might want to treat such a woman with respect.

The special honor we show to Mary is not to be confused with the singular and highest honor due to God. To be specific: We worship and adore God alone (latria, Greek for worship). We honor Mary in a unique way (hyperdulia) as Mother of God and foremost saint (sancta, holy person). We show proper veneration (dulia) to all the saints, since by their lives they demonstrate the activity of God in the world. In the end, all of these forms of honor are directed toward God as manifest to us in various ways and degrees through the response of these holy ones. 

For many Catholics, these ideas have translated throughout history into a desire to engage these signature personalities and benefit from their guidance and example. Devotions toward homegrown saints or particular facets of Mary's life sprang up spontaneously and fulfill a need to connect with our more accomplished fellow travelers among "the communion of saints," as we say. We are sisters and brothers in faith whether living on earth or in heaven, as our belief in eternal life declares. If you had a talented and well-connected relative who could mentor you in your given field, wouldn't you take advantage of that relationship? As we share a common vocation to be saints, having ready-made saints to lean on and get help from is a benefit many are glad to have.

Scriptures: Acts of the Apostles 20:32; 26:18;2 Corinthians 13:12; Ephesians 1:1-2; 5:27; 1 Thessalonians 3:13;  2 Thessalonians 1:10; 2 Timothy 1:9; 1 Peter 2:9; Revelation 18:20

Books: Saints: Men and Women of Exceptional Faith - Jacques Duquesne (Paris: Flammarion, 2012).                            Dictionary of Mary - ed. Alphonse Bossard, S.M.M., transl. John Otto (New York: Catholic Book Publishing Co., 1991).