Input (grade 13): The majority of Christians keep Sunday as a day of worship and rest, every week commemorating the Resurrection of Jesus on the first day of the week on the Jewish calendar.
Output (grade 10): It is there to remember the Resurrection of Jesus on the first day of the week on the Jewish calendar. This is not the first time Christians assembled together on a Sunday; Jesus appeared to the Christians on the "first day of the week" while they were in hiding.