The account of Cornelius’ conversion in Acts 10 does not support the false doctrine of “faith only salvation.” If one actually reads the entire book of Acts, by the time he gets to chapter 10 he has already read of thousands of people who were required to be baptized in water for their sins to be forgiven. In Acts 10 and subsequent chapters the reader will find even more people who were required to do the same. In fact, Luke had already recorded the purpose of water baptism in Acts 2:38, 40 (for the forgiveness of sins, to be saved).
The following are some slides from a sermon on this topic. This first one shows that the requirements for salvation were the same in Acts 2 (speaking to the Jews on Pentecost) as they were in Acts 10 (Cornelius, Gentiles).
The same pattern is seen clearly throughout Acts:
If a person really wants to know what God requires of Him, he will diligently search the Scriptures and find the harmony in all that God revealed (Acts 17:11; 1 Thessalonians 5:21; 2 Timothy 2:15). It would be terrible negligence to ignore what one has already read in Acts and come to some conclusion in Acts 10 that does not harmonize with the rest of Acts, nor the entirety of the Scriptures. God requires more than faith alone, and any honest person who examines the evidence should be able to see that (Luke 8:15).
Passages emphasizing faith or grace in the New Testament were usually written with the purpose of convincing unbelievers that Jesus is the Son of God or teaching people not to keep works of the Law of Moses to be justified under this New Covenant. Context must always be considered! Nobody today has to obey Moses (Matthew 17:1-4; Romans 7:1-4,7; Galatians 5:4; Colossians 2:14-17), but nobody today will become saved until he believes in and obeys Christ (Matthew 7:21-27; Acts 10:35; Romans 6:16-18; Colossians 2:11-13; Hebrews 5:9; 1 Peter 1:22).