On the words of Christ, John 7, 37: “If any man thirst, let him come unto Me and drink,” Luther offers this comment: “These are the two subjects on which we preach. The Law produces thirst; it leads the hearer to hell and slays him. The Gospel, however, refreshes him and leads him to heaven.”
Luther speaks of this difference not only when explaining passages in which the terms Law and Gospel occur, but wherever he has an opportunity to preach these “two subjects.” “The Law tells us what we are to do and charges us with not having done it, no matter how holy we are. Thus the Law makes me uncertain; it chases me about and thus makes me thirsty.”
Now, when Christ invites those who thirst, He means such as have been crushed under the hammer-blows of the Law. Directly Christ invites only these to come to Him; indirectly, indeed, He invites all men. A person thus thirsting is not to do anything but drink, that is, receive the consolations of the Gospel. When a person is really thirsty and is handed but a small glass of water, how greatly refreshed he feels. But when a person is not thirsty, you may fill one glass of water after the other for him, and it will do him no good; it will not refresh him.
Luther proceeds: “The Law says: ‘Thou shalt not kill.’ Its whole urging is directed towards what I am to do. It says: Thou shalt love God with all thy heart and thy neighbor as thyself. Thou shalt not commit adultery, nor swear, and not steal. And then it speaks out thus: See that you have lived or are now living according to what I command you to do. When you have reached this point, you will find that you do not love God with your whole heart as you should, and you will be forced to confess: O my God, I have not done what I should; I have not kept the Law, for neither did I love Thee from my heart to-day, nor will I do so to-morrow. I make this same confession year after year, viz., that I have failed to do this or that. There seems to be no end to this confessing of my trespasses. When will there be an end of this? When shall I find rest unto my soul and be fully assured of divine grace? You will ever be in doubt; to-morrow you will repeat your confession of to-day; the general confession will always apply to you. Now, where will your conscience find rest and a foothold because you assuredly know how God is disposed towards you? Your heart cannot tell you, even though you may be doing good works to the limit of your ability. For the Law remains in force with its injunction: Thou shalt love God and man with your whole heart. You say: I am not doing it. The Law replies: You must do it. Thus the Law puts me in anguish; I have to become thirsty, feel a terror, tremble, and exclaim: How am I to act in order that God may lift up His gracious countenance upon me? I am to obtain the grace of God, but on condition that I keep the Ten Commandments, that I have good works and many merits to show. But that will never happen. I am not keeping the Ten Commandments, therefore no grace is extended to me. The result is that man can find no rest trusting in his good works. He would be glad to have a good conscience. He yearns for a good, cheerful, peaceful conscience and for real comfort. He thirsts for contentment. That is the thirst of which Jesus speaks. It lasts until Christ comes and asks: Would you like to be at ease? Would you like to have rest and a good conscience? I advise you to come to Me. Dismiss Moses and no longer think of your own works. Distinguish between Me and Moses. From Moses you have the thirst which you are suffering. He has done his part for you; he has discharged his office to you; he has put you in anguish and made you thirsty. I am a different Teacher: I will give you to drink and refresh you.”
A person who has not been put through this experience is a sound without meaning (sine mente sonans), a sounding brass and a tinkling cymbal. But a preacher who has personally passed through this experience can really speak from the heart, and what he says will go into the hearts of his hearers. It is a mere accident when some one is awakened from sin and converted by a preacher who is himself unconverted.
Accordingly, when preparing to preach, the preacher must draw up a strategical plan in order to win his hearers for the kingdom of God. Otherwise the hearers may say of his sermon, “Oh, that was nice!” but that will be all. They will leave the church with an empty heart.