In my observation, there are few issues that Christians are more ignorant about than the biblical laws concerning Sabbath. I don't mean to use the word 'ignorant' in a derogatory way. They are not willfully ignorant, but they really don't know the facts of the matter.
So let's get four things straight.
First, the Sabbath, in the Old Testament law, was Saturday. The 4th Commandment was about Israel resting from physical labor and corporately focusing on their relationship with Yahweh. The law specifically stated that they were to work the other 6 days of the week (Sunday-Friday).
Second, the early church seems to have met daily, but they especially celebrated on Sunday because that was the day that Jesus rose from the dead. Of course, most of the early Christians were Jewish, so they continued to honor their cultural heritage by keeping the Saturday Sabbath as well (perhaps this was the invention of the 2 day weekend!).
Third, as the church became more and more Gentile in nature (no Sabbath tradition), Sunday became the main day of corporate worship. Simultaneously, because the church was becoming less and less Jewish in nature, Saturday Sabbath kept fading away.
Fourth, within a few centuries, the transition from Saturday to Sunday was so thorough, that many Christians just assumed that Sunday was the Sabbath Day referred to in the Old Testament. Because of this misconception, they applied some of the legal requirements of Sabbath (like 'do no work') to their Sunday practice.
In our time, this confusion continues. Many Christians today think that Sunday is the Sabbath and that they are legally bound by the 10 Commandments to do no work on that day. Indeed, they might even get upset when they see other Christians unnecessarily working on the Sabbath.
But the facts of the matter are this: The 4th Commandment was a ceremonial law that was fulfilled in Jesus (it no longer directly applies). In the New Covenant, every day is recognized as holy. We are commanded to come together for worship... and it makes sense to do that on the day Jesus rose from the dead... but there are no legalistic laws attached to Sunday worship.
That being said, the principle behind Sabbath law is important and enduring. It makes good, practical sense for Christians to make sure they have times of rest for their body and re-focusing for their soul. When and how this takes place in each believer's life is a matter of freedom.