Complex sentence: Observance of this Sabbath was on the seventh-day of the lunar week which was determined by regularly counting intervals of seven days from after the first day of the month on the Jewish calendar.
Split into simpler sentences: Observance of this Sabbath was on the seventh-day of the lunar week. The Sabbath day is the seventh-day according to and this was determined by regularly counting intervals of seven days from after the first day of the month on the Jewish calendar.