How do we know that the gospel is powerful for salvation?

In this sermon, the preacher emphasizes the gospel as God's power unto true salvation, specifically pointing to the work of Christ crucified. The gospel reveals the reality of our bondage to sin and Satan—illustrated by the desperate situation of the boy in the story. Jesus casting out the demon serves as a picture of the spiritual deliverance that the gospel provides. Romans 1:16 states, 'For I am not ashamed of the gospel of Christ: for it is the power of God unto salvation to every one that believeth.' This underscores that true salvation is not a mere chance for redemption, but a definitive act of God through Christ's sacrificial death—a deliverance from sin and self, made effective by faith.