Original: They argue that the custom of meeting for worship on Sunday originated in paganism, specifically Sol Invictus and Mithraism (in which sun-god worship took place on Sunday) and constitutes an explicit rejection of the commandment to keep the seventh day holy.
Simplified: They argue that the custom of meeting for worship on Sunday originated in paganism, specifically Sol Invictus and Mithraism (in which sun-god worship took place on Sunday).