The 4th Commandment is the Most Important

Much confusion surrounds the issue of the 10 Commandments. Christians are all over the map as to their views of them. Where I grew up, the 10 Commandments were certainly elevated above other commandments; they were revered; we fought for the legal right to have them on plaques in courthouses. Yet there was ambiguity, because no one I knew strictly followed the 4th one (the keeping of the Sabbath). So do we "have to" follow the 10 Commandments today? No, we don't. 

And yes, we do. 

The Old Testament Law, in which the 10 Commandments reside, was the authority of the Old Covenant, and was set aside when the New Covenant was enacted. As for dividing the law into 3 categories- civil, moral, and ceremonial- there really isn't much Biblical evidence for that, as the New Covenant theologians have pointed out. Even the fact that the 4th commandment (a "ceremonial" law) was housed within the other 9 great Commandments (which were all moral), makes this evident. The divisions are not so easy to make. Is the 5th Commandment (honoring parents) moral, while the punishment for breaking it (death) civil?? (One reason Christians who follow the OT Law don't make sense. They leave out the enforcement of the OT Law, which has to include OT punishment, if it's really going to be kept.) "No inspired writer makes any distinction between the "moral" law and the "ceremonial" law." (see source below)

"Now before faith came, we were held captive under the law, imprisoned until the coming faith would be revealed. ²⁴ So then, the law was our guardian until Christ came, in order that we might be justified by faith. ²⁵ But now that faith has come, we are no longer under a guardian, ²⁶ for in Christ Jesus you are all sons of God, through faith." Gal 3

"But as it is, Christ has obtained a ministry that is as much more excellent than the old as the covenant he mediates is better, since it is enacted on better promises.... In speaking of a new covenant, he makes the first one obsolete. And what is becoming obsolete and growing old is ready to vanish away." Heb 8:6, 13

7Now if the ministry of death, carved in letters on stone, came with such glory that the Israelites could not gaze at Moses’ face because of its glory, which was being brought to an end, 8will not the ministry of the Spirit have even more glory? 9For if there was glory in the ministry of condemnation, the ministry of righteousness must far exceed it in glory. 10Indeed, in this case, what once had glory has come to have no glory at all, because of the glory that surpasses it. 11For if what was being brought to an end came with glory, much more will what is permanent have glory. 2 Corinthians 3

What was etched in stone that Moses brought down from the mountain? That's right! The 10 Commandments!

Does this mean we don't have to follow the 10 Commandments? Hardly. In fact, 9 of them are repeated in the New Testament, therefore, we are still to obey them under the New Covenant. This is how often they are repeated in the NT...

1). To worship the Lord God only (1st commandment): no less than 50 times2). Idolatry (2nd commandment): condemned 12 times3). Profanity (3rd commandment): condemned 4 times4). Honoring parents (5th commandment) is taught 6 times5). Murder (6th commandment) condemned 6 times6). Adultery (7th commandment) condemned 12 times7). Theft (8th commandment) condemned 4 times8). False Witness (9th commandment) condemned 4 times9). Covetousness (10th commandment) condemned 9 times
SOURCE 

So those are taken care of. :) What about the Sabbath? I would argue that, in fact, the Sabbath is the most important of all of the Commandments. If you don't believe me, take a look at Hebrews 4. The book of Hebrews sets out to explain to the new Jewish Christians how many things in the Old Covenant were in fact symbols of something coming in the New. 

 "They serve a copy and shadow of the heavenly things." Heb 8:5 and "the law has but a shadow of the good things to come instead of the true form of these realities..." Heb 10:1

The High Priest symbolized Jesus; the sacrifices, the sacrifice of Jesus, and so on. Since the real thing had come, there was no longer a need for the symbol. So what about the Sabbath? The Sabbath symbolized the rest we have in Christ, resting from our works. 

"So then, there remains a Sabbath rest for the people of God, ¹⁰ for whoever has entered God's rest has also rested from his works as God did from his.
¹¹ Let us therefore strive to enter that rest..." Heb 4 and "For we who have believed enter that rest," Heb 4:3

So "there [does] remain a Sabbath rest for the people of God," and it is resting from "our works" and in the finished work of Jesus on the cross (context of Hebrews) for our salvation. 

“Today, if you hear his voice,
do not harden your hearts.” Heb 4:7

Don't forget the most important commandment- in the Old or New Testaments! It's no longer the seventh day of the week, or even the first day of the week, it's ALL the time; it's our very salvation- resting in all God is for us in Jesus!