The Jewish people had many sabbaths, the Jewish people worshiped on Saturday and held the day as holy, but Jesus said that the Sabbath was made for Man and not Man made for the Sabbath, meaning we have power over the Sabbath day. God knows the human body because He made it and He knows it needs a day to rest. As far as the day you can worship any day, but it is best to worship everyday. As Christians we worship on Sunday because that is the day Jesus was resurrected from the dead. He is our Sabbath we find our rest in Him.