The sermon focuses on the contrast between the disciples' lack of faith and the father's mustard-seed faith. After Jesus’ transfiguration, a desperate father brings his demon-possessed son to the nine remaining disciples, but they fail to heal him due to their insufficient faith. Jesus expresses frustration with their lack of spiritual growth, despite their long time of learning under him. The sermon emphasizes the importance of humble faith in Jesus, rather than relying on past experiences or self-reliance. Even faith as small as a mustard seed can achieve great things when it is placed in Jesus, the true "mountain-mover." Ultimately, the object of faith, not its intensity, is what matters.