Is the Sabbath Saturday or Sunday?
Christians gathered on the first day from the earliest records, marking the resurrection. Whether that transfers the fourth commandment or fulfils it is the point at issue.
Scripture: Colossians 2:16-17
Let no man therefore judge you in meat, or in drink, or in respect of a feast day or a new moon or a sabbath day: which are a shadow of the things to come; but the body is Christ's.