Why were the people in Acts 8 baptized when Philip preached?

The people in Acts 8 were baptized because the Jewish message at that time was tied to baptism, and the revelation that baptism has no part in salvation had not yet been given. When Philip preached Jesus Christ, baptism was the natural response, as men and women believed and were baptized.

Les explains that the Jewish message was tied to baptism back then, and that revelation had not yet been revealed. Today baptism has no part in salvation; it must be the finished work of the cross plus nothing. But in Acts 8, that was not the message yet. Philip preached Jesus Christ, and naturally men and women were baptized. Simon himself believed, professed, repented, and was baptized, yet he majored on signs and miracles rather than the person of Christ. Les warns we must be careful and base priorities on Scripture, never making baptism part of salvation, because that would tell God He did not quite finish it.

Why were people in Acts 8 baptized if baptism is not part of salvation?

They were baptized because the Acts 8 setting still belonged to the Jewish message, where baptism was tied to the message being preached. That revelation had not yet been given. Today, however, baptism has no part in salvation; salvation rests on Christ's finished work plus nothing.