The New Covenant does not cancel the Old covenant but rather enables its members to keep the Torah as it says in Jeremiah "and I will write my Torah on the tables of their hearts." (See in Jer. 31 where it talks about the New Covenant.) The early Church fathers (after the Apostles died) disregarded this passage in Galatians and Paul's other writings and assumed that the New Covenant by virtue of it being new set aside and rendered the Old Covenant void. And all of Christianity sadly followed suit. They didn't understand that Yeshua declared in the Gospels "I have not come to abolish the Torah, but rather to fulfill the Torah."
In their Anti-Semetic rush to avoid all things Jewish, they disconnected themsevles from the Schoolmaster which could teach them what sin was, what the penalty for sin was and how G-d would work to change the penalty of sin forever through the coming Messiah.
When the new testament lists sins, Sabbath breaking is conspicuously absent;
In Mark 7:21-22 13 sins are listed. Jesus did not mention breaking the Sabbath.
In Romans 1:29-32 20 sins are listed and not one of them is Sabbath breaking.
In Galatians 5:19-21 a list of 15 sins are given, not one of them is Sabbath breaking.
In 2 Timothy 3:1-4 there's a list of 18 sins, but not once is Sabbath breaking mentioned.
Don't you find it peculiar that nowhere in the New Testament is it taught that the fourth commandment must be observed?