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Erik Raymond writes:
Have you wondered why the Bible repeatedly emphasizes faith as the means by which we receive justification? John Piper begins to walk down this road and think it through in this helpful quote:
“To get at the nature of that faith, it is helpful to ponder why faith alone justifies. Why not love, or some other virtuous disposition? Here’s the way J. Gresham Machen answers this question in his 1925 book What Is Faith? ’The true reason why faith is given such an exclusive place by the New Testament, so far as the attainment of salvation is concerned, over against love and over against everything else in man . . . is that faith means receiving something, not doing something or even being something. To say, therefore, that our faith saves us means that we do not save ourselves even in slightest measure, but that God saves us.’
In other words, we are justified by faith alone, and not by love, because God intends to make it crystal clear that he does the decisive saving outside of us, and that the person and work of Christ are the sole ground of our acceptance with God.”
– John Piper, Think! The Life of the Mind and the Love of God
Already Not Yet 
But how do you define ‘faith’? I know many who define it as a mere agreement to a fact. But does the Bible define it that way?
I would suggest that a study of ‘faith’ would reveal that “trusting obedience” would be a good Biblical definition and ties assurance with conviction that is played out in the life of the believer. Hebrews 11 should show us lots of example of trusting obedience.
The danger in not defining faith is that so many treat like a hope or a wish. That seldom, if ever, will result in a changed life.
Faith is always defined by its object. It’s all about God, his promises, and all he is for us in the person of his Son. Faith is not a work, but what connects us to Christ’s work.