The answer
Saturday was replaced by Sunday during the apostles' time, as it is clear from (Acts 20:7) "And upon the first day of the week (Sunday), when the disciples came together to break bread (communion), St Paul preached unto them, ready to depart on the morrow; and continued his speech until midnight." It is replaced by Sunday because it is the day of Holy Resurrection.Answered by His Eminence Metropolitan Youssef (opens in a new tab)