Matthew 16:19 This verse has been the subject of debate for centuries. Some say the keys represent the authority to carry out church discipline and administration; while others say the keys give the authority to announce the forgiveness of sins. Still others say the keys may be the opportunity to bring people to the kingdom of heaven by presenting them with the message of salvation. The religious leaders thought they held the keys of the kingdom, and they tried to shut some people out. We cannot decide to open or close the kingdom of heaven for others, but God uses us to help others find the way inside. To all who believe in Christ and obey His words, the kingdom doors are swung wide open.
Matthew 16:20 Jesus warned the disciples not to publicize Peter's confession because they did not yet fully understand the kind of Messiah He had come to be - not a military commander but a suffering servant. They needed to come to a full understanding of Jesus and their mission as disciples before they could proclaim it to others in a way that would not cause a rebellion. They would have a difficult time understanding what Jesus came to do until His earthly mission was complete.
Matthew 16:21 The phrase "From that time" marks a turning point. In 4:17 it signaled Jesus' announcement of the kingdom of heaven. Here it points to His new emphasis on His death and resurrection. The disciples still didn't grasp Jesus' true purpose because of their preconceived notions about what the Messiah should be. This is the first of three times that Jesus predicted His death.
Matthew 16:21-28 This passage corresponds to Daniel's prophecies: the Messiah would be cut off (Dan. 9:26); there would be a period of trouble (9:27); and the king would come in glory (7:13, 14). The disciples would endure the same suffering as their King and, like Him, would be rewarded in the end.