When passages from the Old Testament are used to justify or condemn a modern practice, many respond with the all-or-nothing argument, "Well, if you are going to follow the Old Testament on that issue, why not follow it everywhere else — build a rail on top of your roof (Deuteronomy 22:8), do not mix seeds in your garden (Leviticus 19:19), and execute blasphemers (Leviticus 24:11–23)." This often intimidates believers from appealing to the Old Testament. The dreaded all-or-nothing argument always lurks behind the next corner. Of course, some believers never appeal to the Old Testament. Their reason is clear: we live under the New Testament, not the Old Testament. The Old Testament, therefore, is obsolete — or nearly so. It may help us understand the New Testament, but its laws and customs are a bygone product of a bygone Testament.
But a closer reading of the New Testament indicates a different reality. The Old Testament is not obsolete. It has not ceased to be God's Word (2 Timothy 3:16–17). Indeed, how can any word from God become truly obsolete? It may attain fulfillment, but it never becomes defunct. True, New Testament believers do not live under the Old Testament economy, but that does not render the Old Testament obsolete — or even nearly so.
Certainly the book of Genesis still applies to New Testament believers. In fact, it is still authoritative for Christian belief and practice, as any truly Christian statement of faith demonstrates. And happily, Genesis 9:6 — in its meaning, authority, and application — still determines Christian belief and practice and is essential for a healthy society that values and protects human life.
[Read the rest of the article at Answers in Genesis.]