Evidence that the Catholic Tradition DISPLACED an Earlier Tradition Which Celebrated Baptism on the 7th Day of the Feast of Unleavened Bread

The Holy Week before Easter is called the Week of Unleavened Bread. The 'vigil' of Easter in this Christian calendar is also called the last day of the Holy Week. The fact that during the vigil the ceremony of baptism is performed suggests a possible link between baptism and the Crossing of the Sea. [J van Goudouver Biblical Calendars p. 129]

Similarly Clemens Leonard demonstrates in a side by side comparison the idea goes back to Epiphanius' Diataxis and the Syriac Didascalia. In these earliest Semitic traditions Christians and Jews celebrated the week of Unleavened Bread TOGETHER the Jews celebrating and the Christian fasting AGAINST them. These ideas are also demonstrated as being present in Aphraates the Persian Sage (who famously used the Diatessaron).

These sources make absolutely clear that the original Christian tradition not only celebrated the feast of the Unleavened Bread WITH (or against) the Jews but fixed baptism on the seventh day. This tradition was ultimately changed by identifying the week BEFORE Passover leading up as a festival of Unleavened Bread.

Aphraates testimony is of particular interest:

In his Demonstration on Passover, Aphraates the Persian Sage gives another reason why the week before Easter has to be kept. 'When Passover [that is the fourteenth day of the month] falls on a Sunday we must keep it on a Monday [because it was forbidden to fast on a Sunday] so that the whole week can be celebrated with his Passion and with his 'Unleavened.' Because after Passover there follows seven days of Unleavened Bread, until the twenty-first day. When the Passover falls on another day on another day of the week [other than Sunday], we will not be troubled by it. Our festal day is the Friday ... We are bidden to celebrate the feast from its beginning to its end.' [van Goudouver p 178]

Got to go to sleep ...