T. Austin-Sparks emphasizes the significance of the Prophet Isaiah's voice in the New Testament, noting that his prophecies are often linked to Israel's rejection of God's messengers, particularly Jesus Christ. He highlights the tragic irony that despite the frequent readings of Isaiah, many failed to perceive the truth of Christ's presence and message. Sparks warns that true understanding requires spiritual rebirth and the ability to hear with faith, contrasting the blindness of Israel with the enlightenment of those who accept the Holy Spirit's guidance. He challenges listeners to reflect on how the teachings of Isaiah and the prophets have transformed their lives, underscoring the importance of not just hearing but truly understanding and applying God's word. The sermon concludes with a call to recognize the dual nature of prophetic voices, which can lead to both comfort and judgment.