Easter is not only the greatest Christian feast; it is the fulfillment of our faith as Christians. Through His Death, Christ destroyed our bondage to sin; through His Resurrection, He brought us the promise of new life, both in Heaven and on earth. His own prayer, "Thy Kingdom come, on earth as it is in Heaven," begins to be fulfilled on Easter Sunday.
That is why new converts are traditionally brought into the Church through the Sacraments of Initiation (Baptism, Confirmation, and Holy Communion) at the Easter Vigil service, on Holy Saturday evening.
In 2016, Easter Sunday will be celebrated on March 27. Because it is on a Sunday, it is automatically an obligation.