Sabbath Day Changed to Sunday
Although the Bible documents Christ and the disciples keeping the Sabbath on Saturday, nowadays, people associate the day of worship with Sunday.
After Christ’s ascension, the Church continued to grow—spreading even to western regions, including Rome. There, the Church became secularized and adopted pagan customs and teachings. And Rome’s emperor, Constantine, who was also a high priest in the pagan religion, decreed Sunday as the legal day of worship in AD 321 and made Sabbath worship illegal.
“When in 321 Constantine made the first day of the week a holiday, he called it ‘the venerable day of the Sun’ (Sunday).”
The History of Christianity, Time Dowley – Lion Pub. – 1990
From that time, Sunday worship became a common practice in the churches. And this tradition is still seen today. The World Mission Society Church of God, however, bases its teaching solely on the Bible and keeps the original day of worship, Sabbath day on Saturday.