Zac Poonen addresses the issue of spiritual compromise within the church of Thyatira, highlighting the dangers of tolerating false teachings represented by the figure of Jezebel. He emphasizes that while the church had shown growth in deeds, the quality of their faith had diminished due to worldly influences and a lack of strong leadership. Poonen warns against the spiritual adultery that arises from false grace teachings, which lead believers to take sin lightly. He calls for repentance and urges the faithful to hold fast to true grace, promising that those who overcome will be rewarded with authority and the presence of Christ. The sermon serves as a reminder of the need for discernment and steadfastness in faith amidst challenges.