How do we know that the preaching of the Gospel is effective?

The power of the Gospel is affirmed in Romans 1:16, where it states that the Gospel is the power of God unto salvation for everyone who believes. The apostle Paul, during his ministry in Ephesus, demonstrated this as all who dwelled in Asia heard the Word of the Lord through his preaching. Furthermore, God's promise in Isaiah 55:11 guarantees that His Word will accomplish the purpose for which it is sent, thereby affirming its efficacy. The results of true Gospel preaching include the conversion of sinners and the growth of the church, demonstrating God’s sovereign grace in action.