"It is vital to affirm that there is nothing meritorious about faith and that when we say salvation is "by faith not by works" - we are not substituting one kind of merit (faith) for another (works). Nor is salvation a sort of co-operative enterprise between God and us in which He contributes to the Cross and we contribute faith.
No, grace is non-contributory and faith is the opposite of self-regarding. The value of faith is not to be found in itself but entirely and exclusively in it's object - namely Jesus Christ and Him crucified. To say "justification by faith alone" is another way of saying; "Justification by Christ alone".
John R W Stott - "BST Series - The Message of Romans" - IVP, Leicester (1994) - (p117).