RonB, welcome to the forum!

Christians do not keep the sabbath because Christians are not under the law!
Christians are not law keepers, and the law is not a "salad bar" from which we can pick and choose what we like! If we tried to keep part of the law we would have to keep ALL of it, law keepers are UNDER A CURSE as we read here (caps mine):

"For as many as are of the works of the law are under the curse: for it is written, Cursed is every one that continueth not in ALL THINGS which are written in the book of the law to do them. But that no man is justified by the law in the sight of God, it is evident: for, The just shall live by faith. And the law is not of faith: but, The man that doeth them shall live in them. Christ hath redeemed us from the CURSE of the law, being made a curse for us: for it is written, Cursed is every one that hangeth on a tree: That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit THROUGH FAITH." --Gal 3:10-14

RonB, the law is a schoolmaster designed to drive men to Christ, when we come to Christ, God writes his law in our hearts...

"Wherefore the law was our schoolmaster to bring us unto Christ, that we might be JUSTIFIED BY FAITH. But after that faith is come, we are NO LONGER under a schoolmaster."--Gal. 3:24-25

Here is a quick link to Galations chapter 3 so you can read it and see the entire context, ask God to show you the truth from His Word, hope this helps:
http://www.biblegateway.com/passage/...203;&version=9