The Christian websites taught me more about the Sabbath than the Jews did since the jews expect you to and the Christians bother to convince you to, to a much larger extent.
Turns out the Old Testament elaborates on its own reasons for the Shabbat-
1) It is a sign of the covenant betwen God and the Jews and a particular way of connecting to God.
2) it affirms 7 day creation (whether you want to take that literally or not)
3) it is a holy convocation
4) God in Isaiah gives a prosperity blessing to Sabbath keepers.