It is not required for salvation. Before Jesus's resurrection and the ushering in of the New Covenant it was required for salvation. See the context around
Matthew 19:17. It could be a death sentence for breaking the Sabbath law in the Hebrew Scriptures. However, after Pentecost, many of the Jews and Gentiles in the church worshiped on the Sabbath. So, these Gentiles obviously thought it was required. Paul met with Gentiles on the Sabbath in the book of Acts. When they asked him to meet again, Paul instructed them to meet with him the next Sabbath, not on the first day of the week but on the next Sabbath. As the church grew there were those Gentiles who later began meeting on Sunday to honor the resurrection of Jesus. Some claim that happened after the first century CE but I have no way to prove it. In any case, in Paul's time he admonished Christians to not judge each other over days which one esteemed above all others and those who esteemed every day alike. It happens a lot in these discussion forums. Keeping the Sabbath cannot save you. We are saved by grace and that by faith, which is a gift of God. There is no hell awaiting those who serve Yahweh faithfully, no matter what day they keep. I keep the Sabbath, not because it is required to be saved, but because I am happy doing so and I receive bountiful spiritual blessings. It is not a law for our era when it comes to salvation by grace. But that doesn't mean it is a sin to keep it over Sunday. We do know, however, the Sabbath still exists because the Jews keep it and for them it is a perpetual command that was to be served throughout all their generations. We do know, also, that in the Millennium, all nations will observe the Sabbath and pilgrims will come to Jerusalem and worship on the Sabbath. So, during this age of grace we are not required to keep it for salvation purposes. But we have the liberty to keep it as long as we aren't puffed up with pride and look down on our fellow Christians who choose to worship on a different day,