The Bible says:
Hebrews 11:1 New International Version (NIV)
11 Now faith is confidence in what we hope for and assurance about what we do not see.
Romans 10:8-13 New International Version (NIV)
8 But what does it say? “The word is near you; it is in your mouth and in your heart,” that is, the message concerning faith that we proclaim
9 If you declare with your mouth, “Jesus is Lord,” and believe in your heart that God raised him from the dead, you will be saved.
10 For it is with your heart that you believe and are justified, and it is with your mouth that you profess your faith and are saved.
11 As Scripture says, “Anyone who believes in him will never be put to shame.” 12 For there is no difference between Jew and Gentile—the same Lord is Lord of all and richly blesses all who call on him, 13 for, “Everyone who calls on the name of the Lord will be saved.”
John 14:6 New International Version (NIV)
6 Jesus answered, “I am the way and the truth and the life. No one comes to the Father except through me.