The fourth commandment is to honor the Sabbath, to keep it holy. Many people in the church believe that the Sabbath is the seventh day of the week. They would be correct, according to the Bible. It is quite interesting that the common day of worship differs among denominations. Jews and Catholics hold Saturday as the Sabbath, while most Protestants hold Sunday as the day of worship. One major reason for this difference was due to the efforts of the meddling Roman emperor Constantine the Great. This dude was an ardent sun-worshipper before he allegedly converted to Christianity. Therefore, he saw fit to officially change the day of worship to Sunday in accordance with this quaint preoccupation (I am fully aware that it sounds like I am pulling your leg, so I encourage you to look it up). Ever since, that has been the standard for most Protestant denominations. It is also justified by the fact that Jesus raised Himself from the dead on a Sunday.
Since it can become rather difficult and convoluted to reconcile these issues, I will propose my personal solution to the problem. You may have noticed that I modified my UWP calendar app (below) to begin on Monday. This is the way all calendars should be constructed, and I have never heard anyone disagree. We start our workweek on Monday, so that is the first day of the week. Notice that when we make this slight adjustment, Sunday becomes the seventh day. Using this system, Christians can both honor the seventh day and worship on the same day of the week that Jesus rose from the dead. I would go so far as to propose that we have our own calendars printed that use this commonsense system.