The Festival of Passover and Unleavened Bread along with the Festival of Shabuath (Pentecost) were not just Jewish concerns.
Today, few English-speaking Christians, largely due to their long practice of glossing the Hebrew word Phasekh (Passover) with the name Easter and their abandonment of the Festival of Pentecost, realize that Passover and Pentecost were the chief religious observances of the early Christian assemblies.
In one form or another, all early Christian groups not only observed the Passover and Pentecost but calculated the Passover observance in connection with the seven days of Unleavened Bread.