The central message of this sermon is that salvation is not earned or obtained through good works, knowledge, or adherence to a particular system, but rather through a personal relationship with Jesus Christ. The key insight is that knowing about Jesus is not the same as knowing Jesus, and that even those who are considered "good" people still need to be saved through faith in Christ. The sermon highlights the story of Cornelius' conversion, where he and his household were saved simply by hearing and believing the gospel message without any prior works or prerequisites. This challenges the common misconception that one must follow a certain set of rules or laws, such as Moses' law, to have a relationship with God. Instead, Peter preaches that faith in Christ alone is the means of salvation for both Jews and Gentiles, demonstrating that God's love and acceptance are available to all people through Jesus Christ.