Horatius Bonar addresses the disciples' question about greatness in the kingdom of heaven, emphasizing their misunderstanding of entrance into the kingdom. He highlights that true greatness comes from humility and recognizing one's unworthiness, as exemplified by a child. Bonar explains that the way to enter the kingdom is not through merit or personal worth, but through faith and acknowledgment of one's nothingness before God. He contrasts the disciples' pride and ambition with the humility required to truly belong to the kingdom. Ultimately, he teaches that the path to greatness is through becoming the least, following the example of Christ.