Only 26% of Americans read their Bible on a regular basis. Based on observation over the years, those who do read their Bibles spend very little time in the Old Testament. Preachers are in the same boat: even though the Old Testament is 75% of the words of the Bible, only about 20% of sermons are preached from it. So I can say honestly that reading the Old Testament is, relatively speaking, a rarely used way to get to know God better. In Romans 3, the Apostle Paul uses the Old Testament extensively and relates three things it says about God and us.
1. The OT shows the faithfulness of God (verses 1-8). God has proven himself faithful to his creatures by the very act of revealing himself in Scripture. Since we have always rebelled against him, he could have kept his goodness from us. Instead, he freely shows it to us. He showed his faithfulness to Israel in particular. He set them apart as his people, and they were the first to receive his special revelation of himself. Yet they rebelled countless times. The OT records this to show us how God stuck with them. He was always ready to forgive them and bring them home. But one of the primary truths of the OT is that God is faithful to himself and his own justice. In other words, God is willing to forgive sin but not to give a free pass for sin. He is faithful to his people but does not take their sin lightly.
2. The OT shows the depravity of man (verses 9-18). Another certain truth of the OT is that sin is plentiful. Mankind is sick with our own rebellion against God. Paul shows that sin messes up even our understanding–it has twisted us so that we don’t even look to God for forgiveness and guidance. It has poisoned our relationships with others–because of sin we are liars, gossips, and haters. Our sin has also demolished our relationship with God, so that we no longer respect or honor him as God–there is no “fear of God” before our eyes. God cannot have a meaningful relationship with a person who does not honor him as God. So our sin has separated us from him! That leads us to the final, and arguably most important, truth the OT reveals.
3. The OT shows the need for grace (verses 19-20). You might think that once it shows the problem (our sin has alienated us from God) that the OT would give us a hearty dose of encouragement to just do better. Paul points out the problem–sin has broken us so badly that we cannot do better without God’s help. The OT teaches us that we are accountable to God, but its commands do not carry with them enabling power to obey. If so, obedience to the commands could save us. But Paul says it plainly: “By the works of the law no human being will be justified in his sight, since through the law comes knowledge of sin.” So the primary function of the OT is to point out sin, not forgive sin. It is to show the need for salvation. It is to give the promise of salvation. But it does not deliver salvation. Those who lived under the OT had to trust God and believe that he would provide a way. Paul will go on in the following chapters of Romans to show that God provide a way in the person of Jesus Christ. It is only by trusting in him that we can be healed of our sins and restored to God.