You're talking about faith and salvation now. Sounds like what you're saying is that those believers did hear the word of God - that is, they were preached to from the Bible.
Romans 10:17 Faith comes by hearing, and hearing by the word of God.
The word tells us how one is saved:
Romans 10:9
If you confess with your mouth that Jesus is Lord, and believe in your heart that God raised him from the dead, you shall be saved.
That is all that is necessary for salvation - but that does not thorougly equip you for life. The full, complete, revealed word of God (the Bible) will do that. A Christian's life is much better if they are in the word daily, studying it, learning it and applying it. It's all that you need - nothing more!
What the heck is a preacher preaching about if not what the Bible says? If that's not what he's preaching about, then he's not a Christian preacher, he's a motivational speaker, or a psychiatrist, or who knows what...
That's the problem with many churches today. The priests/pastors/preachers don't teach the Bible. Therefore their flock doesn't recognize the truth, and doesn't recognize deceipt and unscriptural teaching when someone tries to pass it off as doctrine.