Luke 9:47 says plainly that Jesus knew “the reasoning of their hearts.” In Matthew 18:1 the situation seems somewhat different. There the disciples come themselves with a question: “Who is the greatest in the kingdom of heaven?” In view of the presence of many disciples and the continuous contact it is not impossible that both incidents took place around the same time. A possible reconstruction could be that the disciples (who on the way have argued about the question who among them was the greatest) now at home ask Jesus the general question who is the greatest in the kingdom. They will then have a secret hope that the answer to that general question will make clear who was right in the special discussion on the way. The pretence fails, however, when from his side Jesus asks another question: “What were you discussing on the way?” The disciples don’t succeed in hiding, by means of a general question, their personal interest in a leading position. Each evangelist portrays this start of the discussion in his own manner (Matthew: by means of the pretence; Mark: by means of Jesus’ revealing question; Luke: with reference to Jesus’ penetrating knowledge).1
33 And they came to Capernaum. And when he was in the house he asked them, “What were you discussing on the way?”