Basically, imagine the Sabbath must have been prior to Moses. That's how we keep it.
Many like to point out the 39 Sabbath restrictions in the Law of Moses (the Torah) and argue that we don't keep the Sabbath because we don't honor those restrictions. We don't observe those things, we believe those ordinances were nailed to the cross. That also applies to festivals, new moons, and dietary restrictions. So, while we observe the Sabbath, we don't believe one should be judged regarding all the Sabbath laws, festivals laws, dietary laws, or laws governing new moons, etc.
Colossians 2:16-17 King James Version (KJV)
16 Let no man therefore judge you in meat, or in drink, or in respect of an holyday, or of the new moon, or of the sabbath days:
17 Which are a shadow of things to come; but the body is of Christ.