"St. Cæsarius of Arles in the sixth century teaching that the holy
Doctors of the Church had decreed that the whole glory of the Jewish Sabbath had been transferred to the Sunday, and that Christians must keep the Sunday holy in the same way as the Jews had been commanded to keep holy the Sabbath Day. He especially insisted on the people hearing the whole of the Mass and not leaving the church after the Epistle and the Gospel had been read." CatholicEncyclopedia
But the seventh day is the sabbath of the LORD thy God:
Exodus 20:10