The work of the ministry labours under one heavy disadvantage when we regard it as a profession and compare it with other professions. In these, experience brings facility, a sense of mastery in the subject, self-satisfaction, self-confidence; but in our subject the more we pursue it, the more we enter into it, so much the more are we cast down with the overwhelming sense, not only of our insufficiency, but of our unworthiness.
Of course, in the technique of our work we acquire a certain ease. We learn to speak more or less freely and aptly. We learn the knack of handling a text, of conducting church work, or dealing with men, and the life. If it were only texts or men we had to handle! But we have to handle the gospel. We have to lift up Christ - a Christ who is the death of natural self-confidence - a humiliating, even a crushing Christ; and we are not always alive to our uplifting and resurrection in Him. We have to handle a gospel that is a new rebuke to us every step we gain in intimacy with it. There is no real intimacy with the gospel which does not mean a new sense of God’s holiness, and it may be long before we realize that the same holiness that condemns is that which saves. There is no new insight into the Cross which does not bring, whatever else come with it, a deeper sense of the solemn holiness of the love that meets us there. And there is no new sense of the holy God that does not arrest His name upon our unclean lips.
If our very repentance is to be repented of, and we should be forgiven much in our very prayers, how shall we be proud, or even pleased, with what we may think a success in our preaching? So that we are not surprised that some preachers, after what the public calls a most brilliant and impressive discourse, retire (as the emperor retired to close his life in the cloister) to humble themselves before God, to ask forgiveness for the poor message, and to call themselves most unprofitable servants--yea, even when they knew themselves that they had “done well.” The more we grasp our gospel the more it abashes us.
From P T Forsyth's The Soul of Prayer, chapter 6