Why do you reject the Sabbath?

Because it was for the Jews only from Mt. Sinai to the resurrection of Jesus Christ. No one had heard of it before Moses came down from Mt. Sinai with the Ten Commandments (Moses wrote Genesis 2:1-3 in the context of Mt. Sinai about 2500 years after creation!). No true Christian kept the seventh day after the Lord’s resurrection, for the first day of the week had replaced the Jewish Sabbath, which Jesus had nailed to His cross and taken out of the way (Col 2:14-17; Acts 20:7; I Cor 16:1-2; Rev 1:10).

See Also

Short document against Sabbatarianism: What About the Seventh Day?
Sermon and outline against Sabbatarianism: Christian or Sabbatarian?