"Here, however the instructor is addressing only this certain knowledge that belongs to the essence of true faith, and he does so exclusively without speaking of the carnal darkness and doubt that are also to be found in the believer. How would he be able to speak of this when his sole intention is to formulate for us the true nature and disposition of true faith, and not the nature and disposition of doubt? Doubt is something entirely different from faith. Doubt is always the exact opposite of faith, and it is always an enemy and persecutor of faith. How could the instructor presently address this when he only desires to address what true faith is?
The fact that this is not observed and understood is the actual cause of so many misconceptions regarding the Catechism's description of faith, and of the thousands of erroneous views regarding it that ruminate in the minds of men. All of this will be resolved at once when, by the Lord's own illumination, we understand this matter correctly, namely, that the instructor is describing for us only what the essence of true faith is, and that faith is the exact opposite of darkness, uncertainty, and doubt. All of these are frequently found in the heart of a poor believer, so that he is frequently and very grievously assaulted and plagued by them, and will be greatly opposed by them during his entire lifetime. According to God's adorable and sovereign good pleasure, the one will experience this more than another and will not be delivered from it, except by the strengthening and increasing fortitude of his faith-a faith that by the grace of the Holy Spirit is securely lodged in the inner core of his heart.