Day of rest? Rest from what? What works are Christians bound to that we need "rest"? Christ is our rest.
Imagine you took a job at a company because you needed to work to pay your bills and debts (like we all do). Part of your job is that you get paid vacations. When you want a vacation, you approach the boss and ask to schedule your vacation time and you get that set vacation time off with pay, as a means to rest from your work at that company. As you work there, you grow to love your job. You become friendly with the owner of the company who is your boss. One day, your boss calls you into the office and says "I like you and I have something I want to do for you. I want to give you $50 million so that you can live out your life debt-free and with no expenses. I hope we will remain good friends as well. Do you accept this offer?" You (of course) say "YES!!! Thank you so much! Thank you thank you thank you!!!" But you also add, "You know, working for you has been great and I want to continue. I don't need a paycheck, I will work for free. I want to be part of your company and I want to show you my appreciation by continuing to work for you!" Your boss thanks you and accepts your offer to work for free.
A few weeks later, you approach your boss - no, your friend and say, "Hey, I would like to take next week off as my vacation." Your friend says to you, "OK, so why are you telling me? You don't get 'vacation days' anymore, you are working for free. If you want a day off you can just take it. You don't have a paid job anymore. I can't 'fire' you from a job you don't have. I appreciate your working for free but you have no obligations and therefore no 'vacation days'. You are free. You are free to never come back here again (although I appreciate that you do). So if you want time for vacation just take it."
I think that's how it is for a Christian who wants to keep the Sabbath. They are clinging to the old convention of a set day of rest that was provided under the works-based system of the Law despite the fact that Jesus redeemed us from the debts and expenses of the Law. Jesus is not our task master but our friend. We have no need of "rest" from works that Jesus has already freed us from. Of course, a Christian with a true faith will still take the time to serve Christ and make that his priority but that is not an obligation. It is the natural outcome of a person being thankful for redemption/salvation.
That's how I see the Sabbath. It would feel foolish to me to keep it out of obligation. It's like keeping dietary laws, it is fulfilled in Christ and to keep them is to deny the fulfillment of such laws.
Considering my analogy, imagine if your friend who gave you the $50 million explained what he did to you yet you kept INSISTING that he must approve your "vacation days" and that you take only the limited amount you had before... It would be insulting to him. it would be like saying you don't trust him, you're not grateful for the $50 million, etc. That's how I see it for a Christian to observe the Sabbath as in the 10 commandments. Christ is our Sabbath and we should recognize that and honor that.