Cult groups harp on the idea that the Roman Catholic Church changed the day of Christian worship from Saturday to Sunday; but the accusation is neither historical nor Biblical.
God gave the Jews the 7th day of the week for rest. Saturday, the Sabbath Day, commemorates God’s completion of Creation (Genesis 2:1-3) and God commanded Israel to observe Saturday as a time of rest from their labors (Exodus 20:8-11).
Christians, however, held Sunday as our day of worship from the very beginning of the Church (Acts 20:7; 1 Corinthians 16:2). The Church began on the Day of Pentecost (Acts 2:1), which always falls on a Sunday, exactly 50 days after the Passover Sabbath.
Jews found the rest from their physical labors in a day on the calendar, Christians find their spiritual rest in the Lord of the Sabbath, Jesus (Matthew 12:8; Hebrews 4:9-11). He called everyone tired of struggling to keep the Law of Moses to Come to Me, all you who labor and are heavy laden, and I will give you rest (Matthew 11:28).
Sunday is the first day of the week. It was the day God began His creation of the universe (Genesis 1:5). Sunday, the day of new beginnings, was the day He created light (Genesis 1:5) and the day Jesus, the Light of the World, was raised from the dead (Matthew 28:1; Mark 16:1-2; Luke 24:1; John 20:1).
As Christians, we worship God every day of the week, but Sunday is our primary day for corporate worship through teaching the Word, prayer, taking the Lord’s Supper, and giving thanks.