One of the most commonly deployed arguments against Christianity and the Bible is the misguided belief that God in the Old Testament was different from God in the New Testament. In his book The God Delusion, atheist crusader Richard Dawkins went as far as to state: "The God of the Old Testament is arguably the most unpleasant character in all fiction: jealous and proud of it; a petty, unjust, unforgiving control-freak; a vindictive, bloodthirsty ethnic cleanser, a misogynistic, homophobic, racist, infanticidal, genocidal, filicidal, pestilential, megalomaniacal, sadomasochistic, capriciously malevolent bully.” (You ought to feel dirty just reading that.) I've also seen devoutly anti-God actor/comedian Bill Maher argue with a professing Bible-believer, asking: "Why did Jesus need to come along to correct His Dad?" (Note that the word choice utilized by both men is derisive and provocative by design. They and others like them are not interested in a discussion, but would love nothing more than to cause one of us to lose our tempers and lash out. They believe that the heart of a Christian is filled with hatred, cursing, and cynicism like theirs are, and each of them wants to be the one to expose it. We would do well to remember that and to keep our ways pure by keeping them according to the Word of the Lord, by hiding His Word in our hearts that we might not sin against Him, and by being transformed by the renewing of our minds. If it's not in us, then we don't have to worry about it coming out of us.) We see the same argument, though, arising from within the church, as more and more self-proclaimed ministers of the gospel turn away from the Old Testament.
To address the argument we need to identify the purposes of the Old Testament and its covenant. For our purposes we will focus on two aspects of the Old Testament. The first we can see through a reading of Exodus 19:5-6; Romans 9-11; 1 Peter 2:5, 8-9; and Revelation 1:6. In these scriptures we find that in the Old Testament one purpose of the old covenant was for God to reveal Himself to the world through the Jewish people, choosing them to serve as a holy nation of priests before Him. Under the new covenant brought about in the New Testament, the same purpose is served by the church, not just the Jews, but those who are of the faith of Abraham.
The other aspect of the Old Testament's purpose that we will focus on is spelled out in Romans 3:20-23, 7:7; Galatians 3:19, 24-27; and 1 Timothy 1:9. The Old Testament and the old covenant serve to bring the knowledge of sin, which should then lead us to understand the need for the Savior. So, we see that the Old Testament and its covenant work in harmony with the New Testament to usher in its covenant, whose necessity would go unknown were it not for the old covenant.
One question persists, though. Why did God require the system of sacrifices for the forgiveness of sin in the Old Testament, and discontinue the requirement in the New Testament? The obvious answer is that Jesus satisfied that requirement, rendering further sacrifice unnecessary. However, wouldn't they have been saved by works in the Old Testament then, instead of by faith as in the New? No. According to Psalm 51:16-17; Matthew 5:16-48, 15:7-9; and Romans 4 we learn that the only hope for salvation for all of humanity for all time is faith in the work of salvation provided by God, even before He provided it. The Old Testament sacrifices were a shadow that pointed to the hope of the Savior.
Another persistent question asks why God judged and punished sin in the Old Testament, but not in the New? Ezekiel 18:23, 33:11; Romans 6:23; and 2 Peter 3:9 teach that at no time has God or will God have any pleasure in the destruction of the wicked. One purpose of the Old Testament, though, is to demonstrate that the wages of sin is death, and the wages of sin will always be death, and the worst judgement of all is promised in the New Testament and is still to come. One dangerous belief held by many modern "Christians" is that God's wrath against sin is satisfied even for those who have rejected His Son.
Still another question persists due to a misunderstanding of scripture. Why were only Jews saved in the Old Testament? The often neglected books of the Law actually made provision for the foreigner who wanted to join the Jewish nation, and serve the one God, to do so. We even see examples in Joshua 2 and Ruth, when Rahab, a Canaanite of Jericho, and Ruth, a Moabitess, both found shelter under the wings of the one God. Not only were they brought into the Jewish nation, but both were even brought into the royal family and the very lineage of Jesus.
Without doubt the Old Testament and the New, along with their covenants, are different. It is important, though, that we remember that God does not change, and that both testaments have their purposes and will always be absolute truth. Every Word of God is pure. We must study the Bible as a whole. We must preach and teach the Bible as a whole with diligence and faithfulness, and without apology or exception. Jesus Christ is the same yesterday and today, yes and forever (Hebrews 13:8).