To go along with the preposition point, here's a quote from Horatius Bonar in Not Faith, But Christ ...
“Faith is not our saviour. It was not faith that was born at Bethlehem and died on Golgotha for us. It was not faith that loved us, and gave itself for us; that bore our sins in its own body on the tree; that died and rose again for our sins. Faith is one thing, the Saviour is another. Faith is one thing, and the cross is another. Let us not confound them, nor ascribe to a poor, imperfect act of man, that which belongs exclusively to the Son of the Living God.
Our security is this, that it matters not how poor or weak our faith maybe: if it touches the perfect One, all is well. God has asked and provided a perfect righteousness; He nowhere asks nor expects a perfect faith. So a feeble, very feeble faith, will connect us with the righteousness of the Son of God; the faith, perhaps, that can only cry, ‘Lord, I believe; help mine unbelief.’ “