As Paul completes the full circle of his argument that all have sinned, he starts Romans three by rhetorically answering questions he knew would come up from those who wanted to find flaws in the argument. However, he ends with a heavy charge: "they are all under sin," using passages from the Old Testament to show the full depravity of mankind. As hard as it is to hear this truth, without it we won't understand the amazing grace of God that Paul will now lay out in the courtroom of God!