The Keys of the Kingdom

 And I say to thee: That thou art Peter; and upon this rock I will build my church, and the gates of hell shall not prevail against it. And I will give to thee the keys of the kingdom of heaven. And whatsoever thou shalt bind upon earth, it shall be bound also in heaven: and whatsoever thou shalt loose upon earth, it shall be loosed also in heaven. (Matthew 16: 18-19)

"Lowly yet Chosen" just like Mary and Joseph. To quote the Catholic World Report:

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.

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