I say Christianity here with a huge grain of salt. The Catholic Church, more specifically, decreed this change and the Protestant churches which sprang from Catholicism have held tight to this belief, regardless of its complete opposition to Biblical command.
Search the Internet for Canon 29 of the Council of Laodicea and you’ll see the following declaration from the Catholic leaders and Emperor Constantine, time frame 364 AD (notice, hundreds of years after the death of Messiah’s Torah-keeping Apostles):
Christians must not judaize by resting on the Sabbath, but must work on that day, rather honouring the Lord’s Day; and, if they can, resting then as Christians. But if any shall be found to be judaizers, let them be anathema from Christ.
A Christian shall not stop work on the Sabbath, but on the Lord’s Day.
Here the Fathers order that no one of the faithful shall stop work on the Sabbath as do the Jews, but that they should honour the Lord’s Day, on account of the Lord’s resurrection, and that on that day they should abstain from manual labour and go to church. But thus abstaining from work on Sunday they do not lay down as a necessity, but they add, “if they can.” For if through need or any other necessity any one worked on the Lord’s day this was not reckoned against him.
Notice how they don’t declare there is a new “Sabbath” but continue to refer to the 7th Day as the Sabbath. They are declaring the Sabbath to be exclusively for Jews and in opposition to anyone claiming to be a Christian. They created a new day to “worship” (rather than Sabbath rest and ceasing from work) and called it “the Lord’s Day”. Conveniently this was, at that time, already a well-established worship day for the majority of pagan peoples, worshiping the Sun god on Sunday.
Remember how YHWH says the Sabbath is to be observed by His people “throughout their generations” and FOREVER? And, remember the verses about not adding to or taking away from His Words? I believe it is clear that those who made this change and those to follow it when they KNOW the Truth about it, are committing a serious sin and acting in opposition to our Creator!
Yes, Sabbath is important for all those who believe in the God of Abraham, Isaac and Jacob AND those who trust in Messiah Yeshua. It is a big deal to our Elohim and thus, it should be a big deal to us!