Isn’t remembering the Sabbath a perpetual moral duty?

Answer:

In speaking to the Gentiles about their salvation in Christ, Paul stated, "And you, being dead in your trespasses and the uncircumcision of your flesh, He has made alive together with Him, having forgiven you all trespasses, having wiped out the handwriting of requirements that was against us, which was contrary to us. And He has taken it out of the way, having nailed it to the cross. Having disarmed principalities and powers, He made a public spectacle of them, triumphing over them in it. So let no one judge you in food or in drink, or regarding a festival or a new moon or sabbaths, which are a shadow of things to come, but the substance is of Christ" (Colossians 2:13-17). Thus Paul is telling the Gentiles that they are not obligated to follow the Old Laws because they had been removed. Besides, these things which so many place emphasis on were merely shadows of something greater under Christ.

Now, in order for someone to claim that having a day without work is a moral duty, they must first prove that this was God's requirement on Christians. Paul makes it clear that Sabbaths went away along with food regulations, the various festivals, and the new moon celebration. Yes, these things were shadows of something in the New Law, but it does not mean all the details about the event also carried over.

For example, the Passover meal foreshadowed Christ's death on the cross. "Therefore purge out the old leaven, that you may be a new lump, since you truly are unleavened. For indeed Christ, our Passover, was sacrificed for us" (I Corinthians 5:7). But this doesn't imply that Jesus needed to be sacrificed every year on the fifteenth day of the first month as the Old Law required for the Passover Lamb. "For the law, having a shadow of the good things to come, and not the very image of the things, can never with these same sacrifices, which they offer continually year by year, make those who approach perfect" (Hebrews 10:1). If there was no difference between the shadow and the substance, then there would be no substance.

There is no mention of Christians being required to set aside a day every week to do no work. To do so would then be adding something to God's law that does not exist. "Do not add to His words, lest He rebuke you, and you be found a liar" (Proverbs 30:6).

Yet, the Sabbath did foreshadow something in the New Covenant.

"Therefore, since a promise remains of entering His rest, let us fear lest any of you seem to have come short of it. For indeed the gospel was preached to us as well as to them; but the word which they heard did not profit them, not being mixed with faith in those who heard it. For we who have believed do enter that rest, as He has said: "So I swore in My wrath, 'They shall not enter My rest,'" although the works were finished from the foundation of the world. For He has spoken in a certain place of the seventh day in this way: "And God rested on the seventh day from all His works"; and again in this place: "They shall not enter My rest." Since therefore it remains that some must enter it, and those to whom it was first preached did not enter because of disobedience, again He designates a certain day, saying in David, "Today," after such a long time, as it has been said: "Today, if you will hear His voice, Do not harden your hearts." For if Joshua had given them rest, then He would not afterward have spoken of another day. There remains therefore a rest for the people of God. For he who has entered His rest has himself also ceased from his works as God did from His. Let us therefore be diligent to enter that rest, lest anyone fall according to the same example of disobedience" (Hebrews 4:1-11).

The writer of Hebrews tells us that there is still a promise of rest awaiting Christians in the future when they can cease from their labors. The writer is talking about the promise of heaven. This is discussed in detail in "Why does Hebrews 4:9 speak of the Sabbath rest remaining if the Sabbath observance is no longer required?"