Today, the jews observe the Passover one day later than did Moses, Nehemiah and Jesus Christ and His disciples. Most of the Jews in Palestine in Christ’s day were also keeping the wrong day – beginning the Passover on the 15th of Abib, which is the 1st Day of Unleavened Bread. Why? When did the Jews lose track of the correct day?
At the time of ezra and Nehemiah, the Jews were still keeping the Passover on the 14th of Abib (Ezra 6:19). In Ezra 6:22, the Days of Unleavened Bread are mentioned as a separate event. So at this time (around 519 B.C.), the Jews were still keeping these days properly.
The confusion occurred when the Jews in Palestine were under control of the Egyptians from about 301 to 198 B.C. – after Ezra’s time, but prior to the time of Christ. The Egyptians allowed the Jews to retain their calendar, but the Egyptians began days at sunrise.
Over time, instead of begining days at sunset as God does, the Jews adopted the Egyptian custom. This change in the start of the day caused the Jews to begin keeping Passover (which is to be observed at sunset) on what the Egyptians referred to as Abib 14 – while on God’s calendar, it was actually the beginning of Abib 15.
Even later on, when the Jews finally got back to an evening-to-evening reckoning for the day, they refused to abandon what had become the traditional way of observing Passover.
The Apple Of God's Eye 