Here are some excellent resources on the sanctity of the Lord’s Day:
1. In order to understand the basic doctrine of the Lord’s Day, I would begin by studying the succinct statements in the Westminster Confession and Catechisms. Westminster Confession, Chapter 21, is titled, “Of Religious Worship and the Sabbath Day.” Larger Catechism Questions 115-121 expound the fourth commandment. Shorter Catechism Questions 57-62 do the same. The Confession and Catechisms are available online for free.
2. If you want to go deeper than these basic statements, I would encourage you to read Joseph Pipa’s TheLord’s Day and Walter Chantry’s Callthe Sabbath a Delight. These books provide the biblical basis and practical application of the commandment.
3. There are a variety of free online resources.
Alistair Begg’s sermons on the fourth commandment are available here
David Strain’s article, “A Well-Spent Sabbath,” is worth a read
R.L. Dabney’streatment of the subject is fantastic, although it isn’t easy reading