The parable is about two different reactions to God’s grace. On one hand is the reaction of the lowest of the low—tax collectors, prostitutes, and sinners. On the other hand, you have the seemingly perfect and upright Pharisees. To one group, the mercy expressed in the three Parables of Luke 15—the lost sheep, the lost coin, and the lost son, commonly known as the Prodigal Son—is amazing. It’s a tale of love and grace, even for the vilest of the vile. To the other, it’s a story of stupidity, of frugality, of weakness. If you’ve been around church for any length of time, you know which is which. The Pharisees see this divine grace as completely absurd. The sinners, on the other hand, rejoice in it. The message is pure Gospel: God has pity on those dead in their sins. He receives sinners and eats with them.
Why does the Pastor preach? Scripture explains that the role of preaching the Word of God is how saving faith is created: “How then will they call on Him in whom they have not believed? And how are they to believe in Him of whom they have never heard? And how are they to hear without someone preaching? And how are they to preach unless they are sent? As it is written, ‘How beautiful are the feet of those who preach the good news!’ … So faith comes from hearing, and hearing through the Word of Christ” (Romans 10:14-17). The Augsburg Confession, seeing this connection between the Preaching Office and saving faith, summarizes Scripture on the Office of the Holy Ministry in this way: “To obtain [saving, justifying] faith, God instituted the Office of Preaching, giving the Gospel and the Sacraments. Through these, as through means, He gives the Holy Spirit who produces faith, where and when He wills, in those who hear the Gospel. It teaches that we have a gracious God, not through our merit but through Christ’s merit, when we so believe” (AC V 1-3). The whole reason the Pastor preaches is so saving faith can be created, so we know that “we have a gracious God” who loves us and has saved us from our sin by the death and resurrection of Jesus Christ.