Jon and Justin consider the fourth commandment in depth regarding the Sabbath day. There is some division of opinion--even amongst Reformed types--as to what observance of the Lord's Day should look like. The distinction between the moral and ceremonial law is a factor, as is one's understanding of covenant theology.
Resources:
Our first episode in this series on Law & Gospel Distinction
Our second episode in this series on The Three Uses of the Law
Our first episode in a series on Covenant Theology
Our first of three episodes on Implications of Covenant Theology