Here is a very good sermon manuscript by Bryn MacPhail on a Canadian reformed theology website entitled “Should Christians Keep the Sabbath?” This pretty accurately summarizes our family’s Confessional view on the Lord’s Day, including the “duties of necessity” portion, which is implied by the heads of grain in Mark 2 as well as Luke 14: “Which of you, having a son or an ox that has fallen into a well on a Sabbath day, will not immediately pull him out?” (ESV).
This is core to the exegetical task: When God said something in the Old Testament, we look at what he said about it in the New Testament. We try to interpret Scripture with Scripture to come to a better understanding of the whole counsel of God. For example, in coming to Scripture in this way, we can see that it is okay to eat pork because of Peter’s vision in Acts 10. We must do the same with the fourth commandment and come to it the way Jesus explained it, and not the way the Pharisees explained it.
“whoever relaxes one of the least of these commandments and teaches others to do the same will be called least in the kingdom of heaven…” (see Mt. 5:17-19, ESV)