The Sabbath

"Remember the sabbath day, to keep it holy...." Exodus 20:8

One of the Ten Commandments that people habitually disregard is the commandment to keep the Sabbath holy.If you drive into a mostly Christian town on a Sunday, you'll still see many shops open with people working. Now, when the Lord gave the Ten Commandments to Moses on Mt. Sinai, He specifically said, "Six days shalt thou labor and do all thy work: But the seventh day is the sabbath of the Lord thy God: in it thou shalt not do any work" (Exodus 20:9-10). Pretty straightforward, right? The Hebrew word sabbath even means "rest."
The Sabbath day was originally on a Saturday, the seventh day of the week. The Jews still celebrate it then. However, Christians celebrate the Sabbath on Sunday. Why? Well, the Savior rose on the first day of the week, and so the Sabbath was changed to that day to honor Him.
Some people think that they can go play football and go rollerblading on the Sabbath, but the Lord in Isaiah 58 said to "turn away thy foot from the sabbath, from doing pleasure on my holy day" (v13). This doesn't mean we can't be happy on the Sabbath, but it does mean that you should turn away from worldly pleasures.
Think about God for a moment. You owe your existence to Him. You owe everything you have to Him. All He's asking for is one day out of seven. That's less than 15% of your waking hours. You should make some sort of effort to honor that. Spencer W. Kimball gave an excellent analogy to this end in the Man-Gleaner Manuel for 1964. He said:

"In the U.S. the second Sunday in May is set apart to honor our mothers; the fourth of July to memorialize our independence; everywhere family members have their birthdays. How thoughtless and inconsiderate  would one be thought who would ignore loved ones' birthdays or who would pay no attention to Mother's Day. How disloyal for one to forget the birthday of our nation or to ignore celebration day. And yet one day of seven has been set apart to remember the Lord, as the Sabbath day - a day for rest, for doing good, for service, for spiritual regeneration, for worship of God. Greedy business fills its store windows with Mother's and Father's Day cards, with Halloween wares and valentines, with birthday remembrances, and with Christmas gifts, but how often does it lend its windows to the encouragement of Sabbath honoring?" - The Teachings of Spencer W. Kimball, p218.

One thing that's important to understand is that "The sabbath was made for man, and not man for the Sabbath" (Mark 2:27). I don't think the Lord needs us to worship Him or that he cares which day we worship Him. However, that doesn't mean we can arbitrarily say, "Oh, I think I'll celebrate the Sabbath on Friday this week and then on Monday next week and..." Not at all! Here's why we must celebrate the Sabbath on a Sunday only (or Saturday only if you're Jewish or a Seventh Day Adventist):
1) It teaches us to keep the commandments. What good is a commandment if you only obey it when it's convenient for you? It's not really a commandment anymore; it's really more of a suggestion. By keeping the Sabbath, we show the Lord that we are capable of doing what He commands when He commands it.
2) We need to go to Church. If you look around at the people at church on Sunday who are there each week, the only ones you will see are active people. No one ever became inactive by habitually attending sacrament meeting. The people you don't see are the inactive ones, and often they fall into apostasy as a result of their inactivity. I know a girl whose parents used to be active in the Church, but the drifted away while she was still young. She really hasn't had that much Gospel training in her life, and now her parents are giving her anti-Mormon literature. That probably wouldn't have happened if they had continued attending church on Sundays.
Now, the only way you can organize a regular sacrament meeting is if everyone plans on it at the same time, which means everyone has to celebrate the Sabbath on the same day.
3) We are creatures of habit. Let's face it: If we have something that we regularly have to do but we do it at random times, we'll probably either a) forget to do it a bunch, or b) fall into a regular pattern. By having the Sabbath on the same day every week, we remember to honor it and we can fall into a routine of what we do on that day.
4) We need to renew our baptismal covenants. I know, this is strictly a member concern, but feel free to keep reading if you're interested. When we partake of the sacrament every Sunday, we renew the covenants we made at baptism. Although none of us are sinless, it's hard to do anything too bad within a week. Attending church helps us to stay on the straight and narrow.

So what kinds of things are acceptable to do on the Sabbath? Well, first off, anything at all honoring the Lord is wonderful. That could mean going to church, doing home/visiting teaching, doing missionary work, or simply reading the scriptures. Anything having to do with the family is also acceptable, provided you don't go do things that would dishonor the Sabbath if you did them yourself. (Here's a hint: if you spend money on a Sunday when it's not a dire emergency - like your tire blows up on the way home from Church and the only way to get home is to fix it immediately -  that's not keeping the Sabbath holy.) Finally, performing service to another such as healing someone or beautifying the neighbor's house - all free of charge - is fine as well.
I hope that you understnad the Sabbath a little better now, and I hope that you'll do your very best to break the trend and keep it! All this I say in the name of the Lord, Jesus Christ. Amen.