Faith is taking God at His word and acting upon it.
This was the summary I came to after my careful study of Faith as shown in the Old and New Testaments. It is interesting how in the Hebrew the word “faith” actually arises from a verb, which we might translate to faith. For people in the Old Testament it was an active thing. What you do shows what your faith is. If you don’t act, then your faith is unreal. This same idea is carried on by Paul (Eph. 2:8-10 as a unit) and James (Jas. 2:15-26) in the New Testament.
God demands faith of His children because if He demanded anything else it would be unfair, since faith is the one thing that all have in common. It is given from the outside “by God” and so has the ability to supersede our fallen intellect and our twisted emotions. Only the person who “faiths” can be justified before God. It doesn’t matter what kind of a mind he or she has, how emotional or unemotional they are. Faith is fundamental and anything less would be our own effort to reach God, and disrespecting the wonderful salvation He offers us.
You can read the full sermon here: Faith: Taking God at His Word and Acting Upon It