In his new book 40 Questions About Christians and Biblical Law, Tom Schreiner concludes his chapter on the Sabbath with this:
Believers are not obligated to observe the Sabbath. The Sabbath was the sign of the Mosaic covenant. The Mosaic covenant and the Sabbath as the covenant sign are no longer applicable now that the new covenant of Jesus Christ has come. Believers are called upon to honor and respect those who think the Sabbath is still mandatory for believers. But if one argues that the Sabbath is required for salvation, such a teaching is contrary to the gospel and should be resisted forcefully.
In any case, Paul makes it clear in both Romans 14:5 and Colossians 2:16–17 that the Sabbath has passed away now that Christ has come. It is wise naturally for believers to rest, and hence one principle that could be derived from the Sabbath is that believers should regularly rest. But the New Testament does not specify when that rest should take place, nor does it set forth a period of time when that rest should occur.
We must remember that the early Christians were required to work on Sundays. They worshiped the Lord on the Lord’s Day, the day of Jesus’ resurrection, but the early Christians did not believe the Lord’s Day fulfilled or replaced the Sabbath. The Sabbath pointed toward eschatological rest in Christ, which believers enjoy in part now and will enjoy fully on the Last Day.
Read more of the biblical and historical reasoning behind his conclusions here.