Gerhard’s Postil for Trinity 8 is fantastic. I recommend the entire sermon! The book is available here. There now follows some choice quotes.
Gerhard first summarizes Nehemiah 4:7-8. Nehemiah orders those working in Jerusalem to keep one hand on their sword and the other hand busy working. Gerhard continues:
You see, this is a perfect image of how church teachers, whom St. Paul depicts as spiritual master builders (1 Cor. 3:10), perform their work and ministry – by building the spiritual Jerusalem, i.e., the Christian Church. Namely, they are not only to finish the building of the spiritual edifice of the Church, but at the same time they are also to fight with the sword of the Spirit – the divine Word – against those who try to hinder the building, and thus drive out all heretics and false teachers. For thus speaks St. Paul in Titus 1:9: “A bishop is empowered to admonish with the saving doctrine and to punish the gainsayers.” Using a different metaphor St. Paul charges the teachers to do this in Acts 20:28. Here he calls them shepherds whom the Holy Spirit has placed over God’s sheep to fertile pastures; but they also must protect them from attack by wolves, as St. Paul exhorts the bishops of Ephesus and, in their name, all church teachers. They must not only tend the sheep allotted to them but must also be alert and look out for wolves, that is, men who teach false doctrine.
Christ Jesus did not come into this world solely to become the Mediator and High Priest and, on the wood of the cross, to pay for the sins of the world, but also to be a teacher and to reveal God’s counsel and will to the human race. This is why in these passages He wishes to hold His example up for all faithful teachers. He not only steadfastly teaches the truth, but He also wishes to punish the Pharisaic and other counterfeit teachings of all times. Subsequently, He held a magnificent sermon for His disciples and those present as a sound beginning for His ministry, as described in chapters 5, 6, and 7 of Matthew. By this He completed a significant portion of His work in building the spiritual Jerusalem; but, observe, with His other hand He reaches for His sword and drives away everything that could hinder this spiritual edifice.
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Since [false prophets’] outward appearance is so gracious, Christ elaborates further on how we must recognize false teachers. He says: “By their fruits you will know them.” This is not to be understood as the external fruits of life, for on occasion false teaching and outwardly impeccable behavior exist together while, conversely, healthy, wholesome teaching and a wicked life can exist together as well, of which Judas, Christ’s betrayer, is an example. Instead, one must distinguish the fruits of doctrine in and of themselves, whether they are good or evil, as is explained in Luke 6:43-44. If the fruits of doctrine are good, then the doctrine is also good; if they are bad and destructive, then the doctrine is also destructive and misleading.
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Each Christian, in his own right, must be vigilant against false prophets so that he will not follow them. For the Lord is not speaking here to His disciples only, but, as is evident in the beginning of Matthew 5, to all people. He admonishes them all to beware of false prophets. In like fashion in 1 John 4:1 John exhorts: “Beloved, do not believe in every spirit, but test whether the spirits are from God, for many false prophets have gone out into the world.” And in 1 Thessalonians 5:21 St. Paul says: “Test all things, and keep what is good.”
The loss of salvation depends for each of us on whether or not we permit ourselves to be separated from the one true Church by heresy and error. “Anyone who does not have the Spirit of Christ is not His” (Rom. 8:9). However, the Spirit of Christ is solely in the spiritual body, that is, in the Christian Church. Anyone who is not a member of this body cannot have the Spirit of Christ and, therefore, cannot have salvation. This is foreshadowed in Noah’s Ark; anyone who was outside of it had to die miserably in the Great Flood. Hence, the Christian Church is the true Ark of Noah; those who remove themselves from it must suffer eternal destruction. The Christian Church is the sole sheepfold of the Lord; whichever little sheep runs away from it will certainly fall into the jaws of the wolf of the soul, the devil. The man who does not have the Church as his spiritual mother cannot have God as his Father.
One cannot come into the Church Triumphant, into the flock of the elect, unless one first comes from the Church Militant, from the true Church in this life. For this all hangs indivisibly together: the Lord god, His holy Word, right faith, true Church, and eternal salvation. Whoever has the one has all of them together; whoever loses one has lost them all. Therefore, each of us must be on guard with the utmost assiduousness so that we are not led away from God’s Word and the true Church by false prophets.
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Gerhard then gives three tests that identify false teaching.
1. All teaching must be tested and judged according to Scripture.
2. All doctrine is aimed at the benefit and consolation of mankind.
3. Whenever a teaching is in accord with God’s Word, its purpose is God’s glory and man’s wellbeing. Such teaching is also good, and those who proclaim it are good prophets. Conversely, whenever a teaching does not correspond to God’s Word its purpose is not for God’s glory nor man’s consolation; it is false and those who proclaim it are false prophets.
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Christianity does not consist of mere words, in merely confessing Christ and boasting of it, but in action and in deeds. Where there are no good fruits there is also no good tree; where Christ’s life is not present, that is, where there is not Christ’s love, Christ’s humbleness, and Christ’s meekness, there is also not Christ…. In and of themselves special gifts do not make the Christian nor the God-pleasing man. The Lord says that He will tell evildoers he does not know them and will not help them even if they have prophesied in His name, etc…. Hence, everything a man can know, regardless of what it may be, whether it be art, wisdom, and knowledge – even if he were equal to Solomon and were expert in all Scripture and all other human endeavors and willing to sacrifice life and limb – without true love and a true Christian heart he is nothing. This is why a simple layman, in whom true faith is working through pure love, is more pleasing to God than a great scholar in whom there is mere knowledge without love or humbleness. Thus, St. Paul says in Ephesians 3:19 that”…loving Christ is better than all knowledge.”
There is, therefore, nothing more foolish than when one boasts about his skills or other gifts. First of all, they are not his, but God’s. Just as little as a hand can boast about its dexterity is as little as a man can boast about his gifts, for they are mere tools of God. Hence, a man is not more pleasing to god because of his gifts.
Ultimately, a gifted man will be held more rigorously to account; for “…to whom much is given, much will be demanded of him” (Luke 12:48). God will not ask you how many gifts you haven, but how well you have used your gifts.