Sabbath-keeping is not moral, other than the reasoning that we morally must do whatever God says to do even if the thing he says to do is not moral in itself..
God would not grow weary in any way if someone was faithful to refraining from adultery or refraining from murder. Would God ever say that our forbiddance from murder and theft and adultery were troublesome to him like he said sabbath-keeping of Israel was troubling to him?
Isaiah 1:13-14.. Bring no more vain oblations; incense is an abomination unto me; the new moons and sabbaths, the calling of assemblies, I cannot away with; it is iniquity, even the solemn meeting. ..(14).. Your new moons and your appointed feasts my soul hateth: they are a trouble unto me; I am weary to bear them.
How can sabbath keeping be a trouble to God if sabbath keeping in and of itself is moral? Could you see God speaking of their refusal to murder and commit adultery in those verses instead of feast keeping and sabbath keeping? Of course not.
Israel trusted in these things when their hearts were not right. Can that be said about refraining from adultery? No, because refusing to commit adultery is in and of itself moral and can never be part of anything that makes its value into something of no value.
You can hypocritically keep sabbath but you cannot hypocritically refrain from adultery or murder, etc.