By Catherine Harmon
Today Pope Francis’ official coat of arms and papal motto were unveiled at a Vatican press conference. The coat of arms is almost identical to the one he used as Cardinal Jorge Mario Bergoglio of Buenos Aires, except the wide-brimmed cardinal’s hat at the top of the shield has been replaced by a miter, and the papal keys have been added.
From the Vatican Information Service, here are details about the symbols found on Francis’ coat of arms:
The shield has a bright blue background, at the centre top of which is a yellow radiant sun with the IHS christogram on it representing Jesus (it is also the Jesuit logo). The IHS monogram, as well as a cross that pierces the H, are in red with three black nails directly under them. Under that, to the left, is a star representing Mary, Mother of Christ and the Church. To the right of the star is a nard flower representing Joseph, Patron of the Universal Church. With these symbols the Pope demonstrates his love for the Holy Family.
Francis’ papal motto, displayed with the coat of arms, is also the same as the one he used as a bishop; it is “miserando atque eligendo,” which in Latin means “by having mercy, by choosing him.” It is taken from a homily of the Venerable Bede on the call of St. Matthew: “Jesus saw the tax collector and by having mercy chose him as an Apostle saying to him: Follow me.” Vatican Radio explains the significance of this passage to the Holy Father:
This homily, which focuses on divine mercy and is reproduced in the Liturgy of the Hours on the Feast of Saint Matthew, has taken on special significance in the Pope's life and spiritual journey.
In fact it was on the Feast of Saint Matthew in 1953 that a young, seventeen-year-old Jorge Bergoglio was touched by the mercy of God and felt the call to religious life in the footsteps of Saint Ignatius of Loyola.
Episcopal—and papal—coats of arms have a long history in the Church, dating back to the Middle Ages. From the Vatican’s website:
There is an at least 800-year-old tradition for Popes to have their own personal coat of arms, in addition to the symbols proper to the Apostolic See. Particularly during the Renaissance and the centuries that followed, it was customary to mark with the arms of the reigning Supreme Pontiff all his principal works. Indeed, Papal coats of arms appear on buildings and in various publications, decrees and documents.
Popes often used their family shield or composed their own with symbols indicating their ideal of life or referring to past events or experiences, or even elements connected with specific Pontifical programmes. At times, they even added a variant to a shield that they had adopted on becoming a Bishop.Details on Pope Benedict XVI’s papal coat of arms and motto (“Cooperatores Veritatis”—“Co-workers of the Truth”) can be read here. Explanations of Pope John Paul II’s shield and motto (“Totus Tuus”—“All yours”) are here.
In Bernadette's day, the Grotto was a dirty, hidden, damp and cold place. The Grotto was literally called the "pig–sty" because that was where pigs feeding in the area took shelter. It was there that the Virgin Mary, dressed in white, a sign of total purity, chose to appear. The contrast between this damp and obscure cave and the presence of the Virgin Mary reminds us of the Gospel, the meeting of the goodness of God and the poverty of the human person. 
The disgusting mud of the pig–sty symbolizes penance. Bernadette, with her face smeared by the mud, becomes a symbol of the deep love that led Jesus to His Passion. She invites us to see the true nature of sin and observe the ugliness of evil. Tasting the bitterness of the grass in the Grotto, she courageously sought penance and the conversion of sinners. This was no simple act of symbolism. Bernadette suffered the disdain of the crowds, as they misunderstood her actions and lost faith in her. Jesus also was disfigured as he carried the cross. The mob mocked and spat at Him. He carried the weight and sins of the entire world on his battered shoulders. True penance enables us to see ourselves as the sinners that we are, and helps us as we recognize our mutual misery and be more compassionate towards each other.
At the ninth apparition, Mary asked Bernadette to scrape the ground, saying to her "Go to the spring, drink of it and wash yourself there." There is only a little muddy water to begin with, enough for Bernadette to drink. At first this water is muddy and dirty then, little by little, it becomes clear. The spring signifies the cleansing of the human heart, wounded by sin yet healed through prayer and penance. Bernadette was asked what the lady said to her. She replied, "Now and again she would say, 'penance, penance, penance, pray for sinners.' " Praying leads us to the Spirit of God. We understand that sin is contrary to the love of God and revealed to us through the Gospel.
During the thirteenth apparition Our Lady said to Bernadette "Go tell the priests to come here in procession and build a chapel here." The word procession, in Lourdes dialect, means a pilgrimage outside of one's parish into other parishes to meet with the people of God on their journey through life. Here, the nations of the Earth, continents and countries, young and old, the healthy and the sick meet in peace and brotherly love. Here, all languages are spoken, all kinds of music are played. On March 25, 1858, the day of the sixteenth Apparition, Bernadette went to the Grotto, and on the instigation of the parish priest, Abbé Peyramale, asked the Lady for her name. Three times Bernadette asked the question. On the fourth request, the Lady responds in dialect 'Que soy era Immaculada Councepciou' (I am the Immaculate Conception). Bernadette does not understand immediately the meaning of these words. She goes to the parish priest to tell him the Lady's name. He understands that it is the Mother of God who has appeared at the Grotto of Massabielle. Her name, the Immaculate Conception, given at the Grotto sums up the entire message of Lourdes.