Sanctify them through thy truth: thy word is truth (John 17:17)
Whether preacher or believer, the truth is that which liberates. It must be truth proclaimed from our pulpits. Truth feeds the soul of the flock and discerns the condition of their spiritual life. Truth converts the sinner to the way of the Lord. It must be truth proclaimed in the conversation of every believer. Human opinions will be debated. Man’s viewpoints shared. Invitations to church dismissed. Truth, however, always penetrates to the dividing of soul and spirit. Truth always accomplishes the will of God. Truth settles all issues though a man fights against his conscience. Our confession must be truth, for then, and only then, will the war be won by the sword of my mouth (Rev 2:16).
We can expect the blessing of God on our efforts to influence men only when we use the Scriptures for that purpose, but when we do so use them we may look confidently for that blessing. The great thing which we need in preaching is the power of the Holy Ghost, without which our words will be utterly lost. Then we should remember that the Scriptures are the Spirit’s own weapon for conquering men. The word is the sword of the Spirit. It is the sword which the Holy Ghost has forged, which he has given to be used by his servants, which he uses himself in the dispensations of providence, and which we may be positive he will bless. When we are preaching the word we are using the very weapon which the Holy Ghost has put into our hands; and will he not make its strokes effective? Is there any other weapon that can be compared with it? In fact, the Spirit himself is using the sword of his word when he leads us to use it. This is the way in which he conducts his dispensation. It is not outside of men, but in them and through them that he maintains and builds up his kingdom. Then the Spirit is with us when we preach the word, and because it is his word it cannot fail of its effects.
 Thomas Murphy, Pastoral Theology. The Pastor in the Various Duties of His Office (Philadelphia,: Presbyterian Board of Publication, 1877), 158-159.