One must hear the Word as a first step to salvation. Faith comes by hearing the Word of God (Romans 10:17), and without faith it is impossible to please God (Hebrews 11:6). The Word of God has been revealed by the Holy Spirit (1 Corinthians 2:6-12 and Ephesians 3:1-5). The Holy Spirit revealed all truth to the writers of the scriptures (John 16:12,13). Since ALL truth was revealed to them, no truth is left to be revealed after their death. Therefore we can know with certainty that something spoken by a man which is not present in the scriptures is false (Matthew 7:15-20). God has chosen preaching as the route by which the message is taught (1 Corinthians 1:18-25). Please follow the links below for more details regarding the points made in this short paragraph.
Belief: How does one gain a true faith?
To whom was the word revealed?
Qualifications of an apostle