Romans 10:17: "So faith comes from hearing, and hearing by the word of Christ."
The faith that will save a man, has to be according to the word of Christ. Christ told his disciples, "I know that His commandment is eternal life; therefore the things I speak, I speak just as the Father has told Me," John 12:50. The gospel which Jesus delivered to us contains the means of our salvation, and, "there is salvation in no one else; for there is no other name under heaven that has been given among men by which we must be saved," Acts 4:12.
Hebrews 11:6: "And without faith it is impossible to please Him, for he who comes to God must believe that He is and that He is a rewarder of those who seek Him."
Without having heard the gospel of Christ, and believing it, there is no possible way for a man to be pleasing to God, and therefore no way for him to be saved. A man must believe that salvation is in Christ, and that God will save Him if he obeys the gospel. In order to be able to do this, he must first hear the gospel. This is why hearing and belief are essential to the salvation of a man.