Of Justification, XI:2

Faith, thus receiving and resting on Christ and His righteousness, is the alone instrument of justification: yet is it not alone in the person justified, but is ever accompanied with all other saving graces, and is no dead faith, but works by love.

The phrase "the alone instrument of justification" means that faith is the sole means by which the believer is justified. The means is not the basis; it is a vehicle or tool (hence, "instrument"). This faith receives and rests "on Christ and his righteousness;" it is that selfsame Christ and the righteousness thereof that provides the basis.

The Confession also asserts that faith, while "the alone instrument," is not alone in the sense that faith is all there is in the believer. Instead, the whole panoply of saving graces, such as adoption and sanctification, comes along with faith. No believer is "barely" justified. Being in Christ gets one the whole kit and kaboodle.

I imagine that must be one of the rare instances where "kit and kaboodle" enters into otherwise serious theological discussions.

Furthermore, this faith is no mere "dead" faith. It is not bare intellectual assent, or even consent. It is an active and living and loving faith that models Christ to others, which is a necessary outworking of the sanctification that inevitably accompanies justification. Although good Christian works do not contribute to the basis of our salvation they are necessary accompaniments that, so to speak, justify our justification to a watching world. And to ourselves, for they are a witness to the activity of the Holy Spirit within us, providing us an assurance of salvation.

Tomorrow: God's justice and grace demonstrated in the salvation of sinners.