As a followup to what I wrote in my last post, I thought I’d post this gem by Michael Horton.
“Nor is faith’s justifying power located in any inherent quality or virtue of faith itself. Faith is only the instrument rather than the basis for justification: it simply lays hold of Christ and his merits. Hence, the common Reformation formulation of justification: per fidem propter Christum (through faith because of or on the basis of Christ). Strictly speaking, one is not justified by faith but by Christ’s righteousness which is received through faith. Therefore, faith is always extrospective: looking outside of itself. Faith does not arise within the self, but comes to us from the outside, through the preaching of the gospel (Rom 10:17). This means that in the act of justification faith is itself completely passive, receiving a gift, not offering one. The faith that justifies is immediately active in love, honoring God and serving neighbor, but this active love is faith’s fruit, not the act of justifying faith itself. Given our native instincts, we can always turn gospel back into law – in this case, by making faith into faithfulness, the act of receiving into an act of working.
Michael Horton, The Christian Faith: A Systematic Theology for Pilgrims On the Way, pg. 583.