There is no way to learn something new about a subject without also admitting that we didn't completely understand it before. Sometimes this is easy to do, and sometimes it is very difficult. It usually takes some time for the truth to sink in, and often we learn these new things not all at once, but a step at a time. There is a story in the Gospel of Mark that illustrates this. See Opening the eyes, a step at a time by Michael Morrison

Jesus' own disciples, both before and after Pentecost, often didn't understand what the Master was doing. Although they had a perfect Teacher, they often failed to understand him correctly. Nevertheless, Jesus used them. This demonstrated that the disciples' success was a result of God's work, not human achievement. It also gives me hope that God will be patient with my slowness, too. See Disciples who didn't understand by Michael Morrison

Jesus taught about the kingdom of God — but what did he say about it? When we are studying something as important as the central message of Jesus Christ, it is not safe to make assumptions. First-century Jews had various assumptions about what the Messiah would do, but Jesus did not act the way they wanted him to. Their assumptions about the king were wrong, and their assumptions about the kingdom were wrong, too. They wanted the Messiah to bring a physical kingdom, but Jesus brought something different. See The message of Jesus 

Jesus preached the kingdom of God. However, the early church preached mostly about Jesus. Is there a contradiction in this? Did the early church get things turned around, preaching about the messenger but neglecting his message? Let's go back to the four Gospels to see whether the early church's focus on Jesus is compatible with Jesus' own teaching. Did Jesus actually preach about himself? See What Jesus said about himself

How did Paul describe the gospel of Jesus Christ? He is consistent in his focus. See a survey of his writings in What Paul said about Jesus