So it is not irreligious, idle, or superfluous, but in the highest degree wholesome and necessary, for a Christian to know whether of not his will has anything to do in matters pertaining to salvation. Indeed, let me tell you, this is the hinge on which our discussion turns, the crucial issue between us; our aim is, simply, to investigate what ability ‘free-will’ has, in what respect it is the subject of Divine action and how it stands related to the grace of God. If we know nothing of these things, we shall know nothing whatsoever of Christianity, and shall be in worse case than any people on earth…That God’s mercy works everything, and our will works nothing, but is rather the object of Divine working, else all will not be ascribed to God. (The Bondage of the Will, Luther’s Reply to Erasmus)
The above quote shows the value of knowing what ability the so-called free-will has. He calls it a “crucial issue.” Yet today, as with Erasmus of old, people do not think that this is an important issue. They are satisfied to think of souls being saved by faith in some way without understanding the situation. However, that is incredibly dangerous. In many ways the Reformation was over this very issue. It is so crucial that it divides what justification by faith alone really means versus a justification by faith alone that is very close to what Roman Catholicism teaches. If the will is moved by itself apart from the grace of God alone, then at the heart of it there is little difference between that and what Rome teaches. It is when it is taught that the enslaved will cannot believe and cannot receive Christ that people get upset. It is when it is taught that the will must be acted upon by God for the soul to have faith that people get upset. But this is at the very heart and hinge of the Gospel.
Here is a quote from R.C. Sproul that gets to the heart of the situation:
When we speak of justification by or through faith, we mean that faith is the instrumental cause of justification, not its ground. Justification is per fidem (by or through faith) but never propter fidem (on account of or on the ground of faith). Again we view justification as being propter Christum (on account of Christ). Sola fide (justification by faith alone) is theological shorthand for justification by Christ alone. We are justified by grace alone through faith alone because of Christ alone…The faith that links us to Christ is not a meritorious work. Indeed, saving faith is itself a gift of God wrought in us by the Holy Spirit.
When the Reformers spoke of faith as being an instrumental cause, they were using the categories of Aristotle. These are very helpful categories. In his book Faith Alone R.C Sproul gives an excellent analogy of that. We can imagine a sculptor making a statue. There is the material cause (that which something is made of; in this case the stone), the formal cause (the design or idea followed; in this case a sketch for the sculptor), the final cause (the purpose for which something is made; in this case the reason the sculptor acts), the efficient cause (the chief agent doing the work; in this case the sculptor), and then there is the instrumental cause (the means or instrument used to make the sculpture, or the sculptor’s chisel in this case). It helps to take a moment and closely reflect on what happens when someone tries to sculpt a statue. In an effort at clarity, let us put this in a different way. 1) There is a rock that one starts with. That is the material cause. 2) There is a design or an idea that one has that will guide the process. That is the formal cause. 3) There is the purpose for which one has for the item made. That is the final cause. 4) There is the person doing the work or sculpting the stone. That is the efficient cause. 5) Lastly, there is the instrument of tool which the sculptor will use to form the stone. That is the instrumental cause.
Faith is the instrumental cause of salvation which is what the efficient cause (God Himself in salvation) uses for the final cause (the purpose for which something is made, and in salvation it is the glory of God). The soul that is saved, which includes the will, is the material cause. The soul is that which something is made of. The analogy stops at some point because God makes His people willing in the day of His power. But in the day of His power He gives faith and uses it as His instrument to save a soul. There is no power in faith itself and there is no power in the soul to use faith itself. There is no ability in faith or in the soul to use faith by itself. God, the only efficient cause, uses faith as His instrument to make in accordance to His own design and for His own purposes a saved soul that has been renewed in the image of Christ. No soul has the ability or freeness of will to do that. God alone can do that and He only does that by His grace because of Christ. The instrument that He uses (not the human) is faith.
The illustration above is certainly limited as are all illustrations and analogies. But when we think of how Scripture speaks of depraved human beings having hearts of stone, the analogy fits quite well. God must use an instrument to break those hard hearts and then something to mold them as He pleases. He uses instruments to do those things and those things do not work on themselves. In the modern day Arminians and professing Reformed folks want faith or the will to be the efficient cause that does the work and for faith to be the instrument in the hands of man. But the Gospel cannot be twisted to allow for such things. John 1:12-13 tells us that the believing soul has been born of the will of God and specifically not of the will of any man. If God is the efficient cause and not man himself, then assuredly faith is the instrument of God to save and not the instrument of man. This shows us the beauty and glory of the Gospel of grace which not only provides grace, but applies it as well. That is because God does it all.
God Loves... Himself 
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