Why did Pope Francis call the Jubilee Year of Mercy?

On April 11, 2015, right before First Vespers of the Vigil of Divine Mercy Sunday, the Holy Father stood before the Holy Door in St. Peter's Basilica and announced an historic event: an extraordinary Jubilee Year of Mercy. "Jesus Christ is the face of the Father's mercy," Pope Francis says in opening his papal bull Misericordiae Vultus (The Face of Mercy). In this light, "Merciful like the Father" is the motto he chose for the Jubilee Year. It comes from Luke 6:36, "Be merciful just as your Father is merciful."

The extraordinary Jubilee Year of Mercy runs from Dec. 8, 2015, the solemnity of the Immaculate Conception, to Nov. 20, 2016, the solemnity of Christ the King. By calling for the Jubilee Year, Pope Francis has underscored the signature message of his pontificate: mercy.

Mercy is the Holy Father's answer to evil, following the teaching of St. John Paul II who, in his last book, Memory and Identity, wrote "[T]he limit imposed upon evil, of which man is both perpetrator and victim, is ultimately Divine Mercy."
Pope Francis explained, "Here, then, is the reason for the Jubilee: because this is the time for mercy. It is the favorable time to heal wounds, a time not to be weary of meeting all those who are waiting to see and to touch with their hands the signs of the closeness of God, a time to offer everyone the way of forgiveness and reconciliation."

This is also the teaching transmitted by St. Faustina Kowalska (who is mentioned by name in the papal bull) in her Diary:

[Jesus said,] "I am prolonging the time of mercy for the sake of [sinners]. But woe to them if they do not recognize this time of My visitation" (1160). "Before the Day of Justice I am sending the Day of Mercy" (1588). "He who refuses to pass through the door of My mercy must pass through the door of My justice" (1146).