Question. But why is faith rather than any other grace else employed in this act?
Answer First. Because there is no grace hath so proper a fitness for this office as faith. Why hath God appointed the eye to see and not the ear? why the hand to take our food rather than the foot? It is easily answered, because these members have a particular fitness for these functions and not the other. Thus faith hath a fitness for this work peculiar to itself. We are justified not by giving anything to God of what we do, but by receiving from God what Christ hath done for us. Now faith is the only receiving grace, and therefore only fit for this office.
Answer Second. There is no grace that God could trust his honour so safely with in this business of justification as with faith. The great design God hath in justifying a poor sinner is to magnify his free mercy in the eye of his creature. This is written in such fair characters in the word, that he who runs {to it} may read it. God was resolved that his free mercy should go away with all the honour, and the creature should be quite cut out from any pretensions to partnership with him therein. Now there is no way like to this of being justified by faith, for the securing and safe-guarding of the glory of God's free grace, Rom. 3:25, 26. When the apostle hath in some verses together discoursed of the free justification of a sinner before God, he goes on to show how this cuts the very comb, yea throat, of all self-exalting thoughts, ver. 27: ‘Where is boasting then? It is excluded. By what law? of works? Nay: but by the law of faith.’ Princes, of all wrongs, most disdain and abhor to see their royal bed defiled. So jealous they have been of this, that, for the prevention of all suspicion of such a foul fact, it hath been of old the custom of the greatest monarchs, that those who were their favourites, and admitted into nearest attendance upon their own persons and queens, should be eunuchs—such whose very disability of nature might remove all suspicion of any such attempt by them. Truly, God is more jealous of having the glory of his name ravished by the pride and self-glorying of the creature, than ever any prince was of having his queen deflowered. And therefore to secure it from any such horrid abuse, he hath chosen faith—this eunuch grace, as I may so call it—to stand so nigh him, and be employed by him in this high act of grace, whose very nature, being a self-emptying grace, renders it incapable of entering into any such design against the glory of God’s grace. Faith hath two hands; with one it pulls off its own righteousness and throws it away, as David did Saul’s armour; with the other it puts on Christ’s righteousness over the soul's shame, as that in which it dares alone see God or be seen of him. ‘This makes it impossible,’ saith learned and holy Master Ball, ‘how to conceive that faith and works should be conjoined as concauses in justification; seeing the one—that is faith—attributes all to the free grace of God; the other—that is works—challenge to themselves. The one, that is faith, will aspire no higher but to be the instrumental cause of free remission; the other can sit no lower, but to be the matter of justification, if any cause at all. For, if works be accounted to us in the room or place of exact obedience in free justification, do they not supply the place? are they not advanced to the dignity of works complete and perfect in justification from justice?’ Treatise of Covenant of Grace, p. 70.
Fourth Particular. The mighty influence, yea universal, that faith hath upon all her sister-graces, speaks her the chief of them all. What makes the sun so glorious a creature but because it is a common good, and serves all the lower world with light and influence? Faith is a grace whose ministry God useth as much for the good of the spiritual world in the saints—called in Scripture the 6"4< 6JÂF4H, ‘the new creation,’ Gal. 6:15—as he doth the sun for the corporeal. Nothing is hid from the heat of the sun, Ps. 19:6, and there is no grace that faith’s influence reacheth not unto.