Dr. A.H. Strong wrote (as cited by me here)
because faith, and not repentance or love or hope is the medium or instrument by which we receive Christ and are united to him. Hence we are never said to be justified dia pistin, = on account of faith, but only dia pisteos, = through faith, or ek pisteos, = by faith. Or, to express the same truth in other words, while the grace of God is the efficient cause of justification and the obedience and sufferings of Christ are the meritorious or procuring cause, faith is the mediate or instrumental cause."
We are not saved or justified by faith in the sense that faith is the ground or reason of it but because it is the means of receiving it.
Louis Berkhof said also:
ReplyDelete"Scripture never says that we are justified dia ten pistin, on account of faith. This means that faith is never represented as the ground of our justification. If this were the case, faith would have to be regarded as a meritorious work of man."
This is from chapter IX - Justification in his Systematic Theology. Others have said the same.