A.W. Pink expounds on 'The Parable of the Mustard-Seed,' emphasizing that the parable illustrates the corrupting influence of worldly systems on the true nature of the Kingdom of Heaven. He argues against the popular interpretation that sees the mustard seed as a symbol of the Gospel's success, instead suggesting that the growth into a tree represents a deviation from the original intent of Christ's teachings. Pink highlights that the 'birds of the air' symbolize Satan and his agents, who find refuge in this corrupted system, indicating a departure from the true essence of Christianity. The sermon warns against the dangers of worldly prominence and the infiltration of falsehood within the Church, ultimately portraying a somber view of the historical development of Christendom. Pink's analysis serves as a call to discernment regarding the true nature of the Kingdom of Heaven amidst the challenges of worldly influence.