The catechetical writing is from the Apology (Defense) of the Augsburg Confession IV (II) 62, 64-67
References are linked to www.bookofconcord.org as well as the whole Book of Concord.
62] Christ, in the last chapter of Luke 24:47, commands that repentance and remission of sins should be preached in His name. For the Gospel convicts all men that they are under sin, that they all are subject to eternal wrath and death, and offers, for Christ's sake, remission of sin and justification, which is received by faith. The preaching of repentance, which accuses us, terrifies consciences with true and grave terrors. [For the preaching of repentance, or this declaration of the Gospel: Amend your lives! Repent! when it truly penetrates the heart, terrifies the conscience, and is no jest, but a great terror, in which the conscience feels its misery and sin, and the wrath of God.] In these, hearts ought again to receive consolation. This happens if they believe the promise of Christ, that for His sake we have remission of sins. This faith, encouraging and consoling in these fears, receives remission of sins, justifies and quickens. For this consolation is a new and spiritual 63] life [a new birth and a new life]. These things are plain and clear, and can be understood by the pious, and have testimonies of the Church [as is to be seen in the conversion of Paul and Augustine]. The adversaries nowhere can say how the Holy Ghost is given. They imagine that the Sacraments confer the Holy Ghost ex opere operato, without a good emotion in the recipient, as though indeed, the gift of the Holy Ghost were an idle matter.
64] But since we speak of such faith as is not an idle thought, but of that which liberates from death and produces a new life in hearts, [which is such a new light, life, and force in the heart as to renew our heart, mind, and spirit, makes new men of us and new creatures,] and is the work of the Holy Ghost; this does not coexist with mortal sin [for how can light and darkness coexist?], but as long as it is present, produces good 65] fruits, as we will say after a while. For concerning the conversion of the wicked, or concerning the mode of regeneration, what can be said that is more simple and more clear? Let them, from so great an array of writers, adduce a single commentary upon the Sententiae that speaks 66] of the mode of regeneration. When they speak of the habit of love, they imagine that men merit it through works, and they do not teach that it is received through the Word, precisely as also the Anabaptists teach at this time. 67] But God cannot be treated with, God cannot be apprehended, except through the Word. Accordingly, justification occurs through the Word, just as Paul says, Rom. 1:16: The Gospel is the power of God unto salvation to every one that believeth. Likewise Rom. 10:17: Faith cometh by hearing. And proof can be derived even from this that faith justifies, because, if justification occurs only through the Word, and the Word is apprehended only by faith, it follows that faith justifies.