According to ancient tradition and canons, the date for the Feast of the Resurrection of Christ (Pascha) derives from and is linked to the ancient Jewish Calendar. This linkage is a result of Christ’s Passion having been directly connected to the Jewish Passover. Strictly maintaining the sequence of events described in the Holy Gospel, the Eastern Orthodox Church always celebrates the Resurrection of Christ after the Jewish Passover, which is being observed this year by observant Jews starting tonight (April 22nd) and ending on the evening of April 30th. The Eastern Orthodox Church will celebrate Pascha this year on May 1st.
From antiquity, the chosen people of the Jews celebrated the Passover in accordance with its lunar calendar, a practice faithfully observed by the Lord Jesus Christ. The Word of God incarnate was a Jew, Who obeyed the requirements of the Old Testament, because He did not come to destroy the Law, but to fulfill it. As the God-Man, Christ fulfilled what was lacking in the Law by offering Himself as a Sacrifice for the redemption of humanity from sin, death, and damnation, becoming thereby a New Passover—”the Sun of righteousness” —for all who believe in Him.
Thus, the Old Testament Pascha, on which the Jews commemorate their Exodus from Egypt, was replaced for the followers of Christ by the New Testament Pascha, celebrating the deliverance of their souls from slavery to the noetic Egypt, that is, sin.