The disciples were unable to cast out a demon and asked Jesus why. Jesus responded that it was because of their small faith, saying that even a tiny amount of faith could move mountains. Jesus then told a parable about a prodigal son who wasted his inheritance and returned home seeking forgiveness. The father welcomed his son back with open arms and celebrated his return, angering the older son who was jealous of the welcome. The parable teaches about God's forgiveness and mercy for those who repent.