From Philo's writings:

{**Yonge's title, A Treatise Concerning the Ten Commandments, Which Are the Heads of the Law.}

XX (96) ”The fourth commandment has reference to the sacred seventh day, that it may be passed in a sacred and holy manner. Now some states keep the holy festival only once in the month, COUNTING FROM THE NEW MOON, as a day sacred to God; but the nation of the Jews KEEP EVERY SEVENTH DAY REGULARLY, after each interval of six days;

"These ten words are summaries of all the laws. For example, the fourth commandment, which deals with the observance of the seventh day, sets forth the principle which regulates all the feasts, including the so-called Passover, when the whole nation dispenses with the priests and on one day in the year celebrates its own sacrifice. "