Complex sentence: Because God rested on the 7th day that is the reason for the observance of the Hebrew Sabbath on the last day of the week the 7th day of the week of the Hebrew Lunar calendar a calendar with 13 months of four weeks each.
Split into simpler sentences: Because God rested on the 7th day, that is the reason for the observance of the Hebrew Sabbath on the last day of the week. The 7th day of the week is indicated on the Hebrew Lunar calendar containing 13 months of four weeks each.