Been doing some studying and finding myself in the Sabbatarian camp, but came across an interesting counter-argument that I haven't seen addressed. There are some who might argue that the Sabbath was still on Saturday, but that the Lord's Day was a separate day we ought to observe and does not carry the full weight of the 4th Commandment. Essentially, how do we know for certain that the Lord's Day was the replacement of the Sabbath, especially when some early Christians celebrated both? Was Christ instituting a New Day to worship him but not to rest? How do we know one way or the other?