A week or two ago a few of the guys from CWC went to a conference on evangelistic preaching from the Old Testament. It doesn't come natural to most, with the vast majority sticking to the gospels or maybe a letter from Paul. But I think that this video helps us to understand what the WHOLE of the Old Testament (and really the whole Bible) is at its root, about.
It totally changes the way we think about preaching, teaching, learning and serving. Jesus is the true fulfilment of all of the Old Testament, something we could not fulfil and still aren't expected to fulfil. It's easy for us to see that we should do things like people in the Bible and then when we can't do it, become depressed. But Jesus could, and did. Jesus came not to abolish the law, but fulfil it (Matthew 5:17), so we could be redeemed from the curse of the law, by him becoming a curse for us (Galatians 3:13). So now, we can live in the light of his grace, being assured that by his death, his righteousness is imputed to us. We now receive God's unmerited favour and that brings us joy.