Because there may be an apparent delay before his return, Jesus told a parable to encourage his disciples. They may suffer injustice from opponents of the gospel, but they must persevere in prayer, confident that God will hear them (Luke 18:1). If an ungodly judge will give a just judgment to a helpless widow solely to be rid of her ceaseless pleading, how much more will the holy God answer the cries of his persecuted people. The world may be unbelieving, but the disciples of Jesus must maintain their faith to the end (Luke 18:2-8).
In the second story Jesus rebuked those law-abiding people who thought their behaviour made them and their prayers acceptable with God. The Pharisee recounted his good deeds, and expected God to be pleased with him. He despised the tax collector, and was sure that God did too (Luke 18:9-12). But the tax collector made no attempt to impress God. He simply confessed himself a sinner and asked God for mercy. God accepted the man who humbly repented, but rejected the one who boasted of his virtue (Luke 18:13-14).