The 2nd Sunday of Easter is Divine Mercy Sunday

John Paul II declared the 2nd Sunday of Easter to be Divine Mercy Sunday as a recognition of the inconceivable mercy of Christ.

In particular this feast day stems from private revelations that St. Faustina received in the early 20th century, where she wrote of Christ's great love for all and his desire to extend mercy to all. The Church teaches that on this particular Sunday special graces of mercy are present in taking the Eucharist, if you have received the sacrament of reconciliation within 20 days of Divine Mercy Sunday. In recognizing Christ's great mercy through our own repentance and desire for mercy the Church teaches that our sins are indeed completely forgiven. The Church also teaches that Christ's mercy compels us to go out and be merciful in our own lives and in the world. 

Check out more info about this feast day at:
http://www.usccb.org/beliefs-and-teachings/how-we-teach/new-evangelization/year-of-faith/notes-and-quotes-for-reflection-on-divine-mercy.cfm