The bible teaches us that the Sabbath day is the last day which God rested and he wants us to also rest. After God created everything and everything was looking good, on the seventh day he rested and mark that day to be holy, which all human is expected to rest on that day after work.
Even in the ten commandments God still add it as a commandments for us not to forget "remember the Sabbath day and keep it holy". In the biblical calendar, the seventh day of the week is what we call Saturday today. This shows that the original Sabbath established by God was the seventh day.
In the new testament when Jesus came to this world he also keep the Sabbath day holy, by using that day to preach the gospel to people. On the Sabbath day Jesus went to synagogue to preach and pray. While some Christians worship on Sunday to remember the resurrection of Jesus, the Bible clearly shows that the Sabbath originally referred to the seventh day, a day meant for rest, worship, and drawing closer to God.
