R.A. Torrey explores the growth of the Kingdom of Heaven through the parables of the seed and the mustard seed, emphasizing the natural and divine processes involved in spiritual growth. He highlights that the seed represents the Word of God, which grows independently and powerfully, while the mustard seed illustrates the Kingdom's humble beginnings and expansive growth. Torrey also discusses the leaven as a symbol of the Gospel's pervasive influence, warning against the corrupting effects of false doctrine within the church. The sermon encourages believers to recognize the significance of their faith and the importance of safeguarding the truth against insidious errors. Ultimately, Torrey reassures that the growth of the Kingdom is both a divine promise and a call to vigilance.