This is an excerpt from Luther’s Large Catechism, in the Book of Concord.
“Comprehend the difference, then, that Baptism is quite another thing than all other water; not on account of the natural quality but because something more noble is here added; for God Himself stakes His honor, His power and might on it. Therefore it is not only natural water, but a divine, heavenly, holy, and blessed water, and in whatever other terms we can praise it, all on account of the Word, which is a heavenly, holy Word, that no one can sufficiently extol, for it has, and is able to do, all that God is and can do (since it has all the virtue and power of God comprised in it).
“Hence also it derives its essence as a Sacrament, as St. Augustine also taught. That is, when the Word is joined to the element or natural substance, it becomes a Sacrament, that is, a holy and divine matter and sign.
“Therefore we always teach that the Sacraments and all external things which God ordains and institutes should not be regarded according to the coarse, external mask, as we regard the shell of a nut, but as the Word of God is included therein … Thus, and much more even, you must honor Baptism and esteem it glorious on account of the Word, since He Himself has honored it both by words and deeds; moreover, confirmed it with miracles from heaven. For do you think it was a jest that, when Christ was baptized, the heavens were opened and the Holy Ghost descended visibly, and everything was divine glory and majesty?
“Therefore I exhort again that these two, the water and the Word, by no means be separated from one another and parted. For if the Word is separated from it, the water is the same as that with which the servant cooks, and may indeed be called a bath-keeper’s baptism. But when it is added, as God has ordained, it is a Sacrament, and is called Christ-baptism. Let this be the first part, regarding the essence and dignity of the holy Sacrament.
“In the second place, since we know now what Baptism is, and how it is to be regarded, we must also learn why and for what purpose it is instituted; that is, what it profits, gives, and works. And this also we cannot discern better than from the words of Christ above quoted: “He that believeth and is baptized shall be saved.”
“Therefore state it most simply thus, that the power, work, profit, fruit, and end of Baptism is this, namely, to save. For no one is baptized in order that he may become a prince, but, as the words declare, that he be saved.But to be saved, we know, is nothing else than to be delivered from sin, death, and the devil, and to enter into the kingdom of Christ, and to live with Him forever.
“Here you see again how highly and precious we should esteem Baptism, because in it we obtain such an unspeakable treasure, which also indicates sufficiently that it cannot be ordinary mere water. For mere water could not do such a thing, but the Word does it, and (as said above) the fact that the name of God is comprehended therein. But where the name of God is, there must be also life and salvation, that it may indeed be called a divine, blessed, fruitful, and gracious water; for by the Word such power is imparted to Baptism that it is a laver of regeneration, as St. Paul also calls it (Titus 3:5).
“But as our would-be wise, new spirits assert that faith alone saves, and that works and external things avail nothing, we answer: It is true, indeed, that nothing in us is of any avail but faith, as we shall hear still further. But these blind guides are unwilling to see this, namely, that faith must have something which it believes, that is, of which it takes hold, and upon which it stands and rests.
“Thus faith clings to the water, and believes that it is Baptism, in which there is pure salvation and life; not through the water (as we have sufficiently stated), but through the fact that it is embodied in the Word and institution of God, and the name of God inheres in it. Now, if I believe this, what else is it than believing in God as in Him who has given and planted His Word into this ordinance, and proposes to us this external thing wherein we may apprehend such a treasure?
“Now, they are so mad as to separate faith, and that to which faith clings and is bound, though it be something external. Yea, it shall and must be something external, that it may be apprehended by the senses, and understood and thereby be brought into the heart, as indeed the entire Gospel is an external, verbal preaching. In short, what God does and works in us He proposes to work through such external ordinances. Wherever, therefore, He speaks, yea, in whichever direction or by whatever means He speaks, thither faith must look, and to that it must hold.
“Now here we have the words: He that believeth and is baptized shall be saved. To what else do they refer than to Baptism, that is, to the water comprehended in God’s ordinance? Hence it follows that whoever rejects Baptism rejects the Word of God, faith, and Christ, who directs us thither and binds us to Baptism.
“In the third place, since we have learned the great benefit and power of Baptism, let us see further who is the person that receives what Baptism gives and profits. This is again most beautifully and clearly expressed in the words: He that believeth and is baptized shall be saved. That is, faith alone makes the person worthy to receive profitably the saving, divine water. For, since these blessings are here presented and promised in the words in and with the water, they cannot be received in any other way than by believing them with the heart.
“Without faith it profits nothing, notwithstanding it is in itself a divine superabundant treasure. Therefore this single word (He that believeth) effects this much that it excludes and repels all works which we can do, in the opinion that we obtain and merit salvation by them. For it is determined that whatever is not faith avails nothing nor receives anything.
“But if they say, as they are accustomed: Still Baptism is itself a work, and you say works are of no avail for salvation; what, then, becomes of faith?
“Answer: Yes, our works, indeed, avail nothing for salvation; Baptism, however, is not our work, but God’s (for, as was stated, you must put Christ-baptism far away from a bath-keeper’s baptism). God’s works, however, are saving and necessary for salvation, and do not exclude, but demand, faith; for without faith they could not be apprehended.
“For by suffering the water to be poured upon you, you have not yet received Baptism in such a manner that it benefits you anything; but it becomes beneficial to you if you have yourself baptized with the thought that this is according to God’s command and ordinance, and besides in God’s name, in order that you may receive in the water the promised salvation. Now, this the fist cannot do, nor the body; but the heart must believe it.
“Thus you see plainly that there is here no work done by us, but a treasure which He gives us, and which faith apprehends; just as the Lord Jesus Christ upon the cross is not a work, but a treasure comprehended in the Word, and offered to us and received by faith. Therefore they do us violence by exclaiming against us as though we preach against faith; while we alone insist upon it as being of such necessity that without it nothing can be received nor enjoyed …
“Thus we must regard Baptism and make it profitable to ourselves, that when our sins and conscience oppress us, we strengthen ourselves and take comfort and say:
Nevertheless I am baptized; but if I am baptized, it is promised me that I shall be saved and have eternal life, both in soul and body.
“For that is the reason why these two things are done in Baptism, namely, that the body, which can apprehend nothing but the water, is sprinkled, and, in addition, the word is spoken for the soul to apprehend. Now, since both, the water and the Word, are one Baptism, therefore body and soul must be saved and live forever: the soul through the Word which it believes, but the body because it is united with the soul and also apprehends Baptism as it is able to apprehend it. We have, therefore, no greater jewel in body and soul, for by it we are made holy and are saved, which no other kind of life, no work upon earth, can attain.”