There is still a sabbath of sorts, but it is on Sunday the first day of the week not Saturnday the seventh…
1Cor 16
1 Now concerning the collection for the saints: as I directed the churches of Galatia, so you also are to do. 2 On the first day of every week, each of you is to put something aside and store it up, as he may prosper, so that there will be no collecting when I come. 3 And when I arrive, I will send those whom you accredit by letter to carry your gift to Jerusalem. 4 If it seems advisable that I should go also, they will accompany me.
Paul here is discussing a gathering for Jerusalem form the Churches in Galatia and in Macedonia. In other words this is a Church gathering and the day Paul instructs the gathering to be taken is on the first day.
So why the change?
Christ was raised on Sunday thus the day became known as the “Lord’s Day,” and we have Biblical proof positive that this practice was extant at the writing of the Apostles…
Revelation 1
9 I, John, your brother and partner in the tribulation and the kingdom and the patient endurance that are in Jesus, was on the island called Patmos on account of the word of God and the testimony of Jesus. 10 I was in the Spirit on the Lord’s day, and I heard behind me a loud voice like a trumpet 11 saying, "Write what you see in a book and send it to the seven churches…
Seems pretty straight forward to me.
Concerning the ceremeonial laws about the Sabbath I think you have to remember that Christ said the sabbath is for men not the men for sabbath, in other words the sabbath is a time given us by God when we can come to worship Him in rest in preparation for the rest in Paradise with God forever. It is a time for us to rest and worship and glorify God. Thus the laws against work were intended to prevent men from using the sabbath as any other day when it was meant for rest and worship. But never to become a burden to men to prevent them from doing anything at all.
That is why the Church recognizes that works of charity and necessity, such as medical, legal, law enforcement, etc are perfectly acceptable on Sunday even though that is work. As also is caring for a sick person in the family and other needful works of charity. If these sort of works are being done it is not a sin to miss Mass, but if a man chooses to miss Mass so he may watch football or mow the lawn or golf or fish that is a sin because it denigrates God’s Law and robs the day of its purpose, namely to be a time of repose when we will all come and worship our God.
So the old laws about the seventh day are set aside in favor of the Lord’s day.
The Lord’s day is to be observed but is not a tyranny.
The Pharisaic understanding of the Sabbath Law was never in effect because it was never a valid understanding of the Law, and thus it is no law at all which needed to be set aside.
God Bless