In a previous post (http://adisciplesthoughts.blogspot.com/2008/05/god-who-knows-heart.html), I mentioned that Cornelius along with his friends and family were accepted by God before they had expressed their faith and obedience. God had seen their faith before they had demonstrated it, and he had accepted them because of it.
So why did Peter order "that they be baptized in the name of Jesus Christ" (Acts 10:48, NIV)? After all, they had been accepted by God. Why did it matter?
First, when we have been saved by God's grace, we become changed people, a people who are "eager to do what is good" (Titus 2:11-14, NIV). We want to do God's will.
Second, Christ wants his disciples to be baptized and to obey everything he has instructed us to do (Matthew 28:18-20). When we accept Jesus Christ as Lord---as the one we depend on and serve---we do what he wants. Since he wants his followers to be baptized, we are baptized.
Third, we need a clear break from our past lives as we enter new lives with Christ. In baptism, our old lives are buried with Christ; we arise from baptism with a fresh start to a new life of following Jesus (Romans 6:1-7).
Finally, we want to accept the benefits attached to baptism. Peter taught that penitent believers would receive the forgiveness of sins (Acts 2:38), the gift of the Holy Spirit (Acts 2:38), and salvation (1 Peter 3:21) when they were baptized.
Cornelius had been changed by God's grace. He was eager to do anything that Jesus demanded of him. When he was told that Christ wanted him to be baptized, he was eager to comply. Cornelius was ready to mark the end of his life without Christ and the beginning of his life with Christ. Knowing that God had accepted him, Cornelius would not reject the forgiveness of sins, the gift of the Holy Spirit, and salvation by refusing to be baptized in the name of his Savior. Why would he?