Matthew 20 talks about Jesus teaching His disciples about service and humility, and the heavenly rewards for those who display these virtues. In the chapter, Jesus also shares the parable of the workers in the vineyard, which teaches about fairness and generosity, and how God does not play favorites. Additionally, the chapter discusses Jesus' prediction of His impending death and the request of James and John to be seated at His right and left hands, which leads to Jesus emphasizing the importance of serving rather than being served.