It was asked in the Baptist section of the site.
Why do we fight for reinstating the ten commandments, when atheists & agnostics tear it down, but then neglect the 4th commandment? Isn't the 4th as valid as the other 9? If the commandments are to be written in our hearts, why do we select the 1st day to be observed, when the 4th commandment specifically mentioned the 7th day? Then again, if the day doesn't matter, why not select Friday, because there wouldn't be a resurrection without a death first, for the sacrificial death of our God is just as important as His resurrection?
This is an Excellent Question!
The answer is that the Sabbath is the only day set aside in the Bible for worship and declared sacred and that was never repealed.
Seventh Day Baptists and a few other groups do honor the Shabbat as my family will be doing so in an hour or so. Shabbat begins today at 4:50 our time.
Here's a good website where you can select a nearby city for your Shabbat times: http://www.sunrisesunset.com
Sunday was selected as the holy day for Christians because that was the day the Pagan world worshiped Sol Invictus, the Sun god and Rome wanted to unite all religions as one.
I have several studies on the Sabbath, how to observe it, how we lost it and how to regain it here http://allfaith.com/Religions/Noahide/shabbat.html if you are interested.
~ John of AllFaith