“For it is by grace you have been saved, through faith–and this not from yourselves, it is the gift of God — not by works, so that no one can boast. For we are God’s workmanship, created in Christ Jesus to do good works, which God prepared in advance for us to do.” Ephesians 2:8-10
Salvation is caused by grace through the means of faith. The purpose of this scheme is so that that no one can boast.
Why should God save those who have faith in Christ? He has no moral or logical obligation to do so. If a criminal goes before a judge who has overwhelming eyewitness and video evidence that he commited a heinous crime, but then says “I know that you are a good judge. I have faith in you, your Honor!” does it follow that the judge should let the criminal go free?
God has ordained that faith in Christ is the vehicle and the means by which His saving grace is actualized in man.
Faith is not a power to be wielded, nor a work that merits a reward from God. No, it is by gracious condescension that God allows faith in Christ to have any effectiveness or merit. A man can neither summon up faith from nothingness, nor increase his faith by his own work or effort. Faith is solely a gift of God’s saving grace. Grace is not a reward for faith; instead faith is the result of grace.
“It is not faith that saves, but faith in Jesus Christ…. It is not, strictly speaking, even faith in Christ that saves, but Christ that saves through faith. The saving power resides exclusively, not in the act of faith or the attitude of faith or in the nature of faith, but in the object of faith.”
– B. B. Warfield