In Hebrews 11, we find the definition of faith—the only word explicitly defined in the Bible. “Now faith is the substance of things hoped for, the evidence of things not seen” (Hebrews 11:1). Here, we see a relationship between faith and hope. Faith is here and now; hope is for the future. Faith is a material thing—something so real that it is called a substance. It is in our hearts. On the basis of faith, we can have a legitimate hope for the future. But hope that is not based on legitimate faith is just wishful thinking.
If you confess with your mouth the Lord Jesus and believe in your heart that God has raised Him from the dead, you will be saved. For with the heart one believes unto…salvation. (Romans 10:9–10)
In the New Testament, believe is a word of motion. It is not a static thing or an intellectual position. It is something in your heart that leads you to something new. Faith is a verb of motion: by faith we believe unto righteousness and salvation. You can have intellectual faith and never be changed. You can embrace all the doctrines of the Bible with your intellect but remain completely the same. But when you have faith in your heart, it leads to salvation.
Faith is in the present; hope is in the future. Biblical faith is in the heart; hope is in the mind. Paul spoke about both with an interesting picture: “But let us who are of the day be sober, putting on the breastplate of faith and love, and as a helmet the hope of salvation” (1 Thessalonians 5:8). Two items of armor are mentioned in this verse. Faith is a breastplate, which protects the heart, and hope is the helmet, which protects the head. Faith is in the heart; hope is in the mind.