According to Berkhof, (see his systematic for the complete article):
Scripture says that we are justified
dia pistis, ek pistis, or pistei (dative) --(Romans 3:25, 28, 30; 5:1, Galatians 2:16; Philippians 3:9, etc). The preposition
dia stresses the fact that faith is the
instrument by which we appropriate Christ and His righteousness. The preposition
ek indicates that faith logically precedes our personal justification. The dative is used in the
instrumental sense. However, Scripture
never says we are justified on account of faith. Faith is
never represented as the ground of our justification--if it was it would be a meritorious work of man (Romans 3:21, 27, 28; 4:3-4, Galatians 2:16, 21, 3:21, etc).
Probably a better name than
instrument would be
appropriating organ. Thus, by faith the sinner appropriates the righteousness of Christ and establishes union between himself and Christ. The merits of Christ constitute the
dikaioma, the legal basis on which the formal declaration of God in justification rests. By faith the sinner appropriates the righteousness of the Mediator already imputed to him ideally in the
practum salutis; and on the basis of this he is now formally justified before God. The phrase
appropriating organ includes the
instrumental idea and is therefore
perfectly in harmony with the statements found in our confessional standards. It has an advantage over the phrase
instrumental cause because it excludes the idea that faith is in any sense the basis for justification. See Hodge (attachment) for more....
There are some excellent articles
here (select: Sola Fide) (Berkhof's is there also)
