Why do Christians follow certain laws from the Old Testament and not others?

Tim Keller recently wrote an article responding to those who might say that Christians are inconsistant with what they follow from the Bible. For example, we do Christians eat pork and shellfish and why do we not execute people for breaking the Sabbath? His explanation is helpful and clear. Here's his conclusion:

Once you grant the main premise of the Bible---about the surpassing significance of Christ and his salvation---then all the various parts of the Bible make sense. Because of Christ, the ceremonial law is repealed. Because of Christ, the church is no longer a nation-state imposing civil penalties. It all falls into place. However, if you reject the idea of Christ as Son of God and Savior, then, of course, the Bible is at best a mishmash containing some inspiration and wisdom, but most of it would have to be rejected as foolish or erroneous.

So where does this leave us? There are only two possibilities. If Christ is God, then this way of reading the Bible makes sense. The other possibility is that you reject Christianity's basic thesis---you don't believe Jesus is the resurrected Son of God---and then the Bible is no sure guide for you about much of anything. But you can't say in fairness that Christians are being inconsistent with their beliefs to follow the moral statements in the Old Testament while not practicing the other ones.

Read the whole thing