Here is a good reminder from Charles Spurgeon on why ministers need to watch their own lives and souls.
Every workman knows the necessity of keeping his tools in a good state of repair, for “if the iron be blunt, and he do not whet the edge, then must he put to more strength.” If the workman lose the edge from his adze, he knows that there will be a greater draught upon his energies, or his work will be badly done. Michael Angelo, the elect of the fine arts, understood so well the importance of his tools, that he always made his own brushes with his own hands, and in this he gives us an illustration of the God of grace, who with special care fashions for himself all true ministers. It is true that the Lord…occasionally makes very foolish preaching to be useful in conversion; and he can even work without agents, as he does when he saves men without a preacher at all, applying the word directly by his Holy Spirit; but we cannot regard God’s absolutely sovereign acts as a rule for our action. He may, in his own absoluteness, do as pleases him best, but we must act as his plainer dispensations instruct us; and one of the facts which is clear enough is this, that the Lord usually adapts means to ends, from which the plain lesson is, that we shall be likely to accomplish most when we are in the best spiritual condition; or in other words, we shall usually do our Lord’s work best when our gifts and graces are in good order, and we shall do worst when they are most out of trim. This is a practical truth for our guidance, when the Lord makes exceptions, they do but prove the rule.
We are, in a certain sense, our own tools, and therefore must keep ourselves in order. If I want to preach the gospel, I can only use my own voice; therefore I must train my vocal powers. I can only think with my own brains, and feel with my own heart, and therefore I must educate my intellectual and emotional faculties. I can only weep and agonise for souls in my own renewed nature, therefore must I watchfully maintain the tenderness which was in Christ Jesus. It will be in vain for me to stock my library, or organise societies, or project schemes, if I neglect the culture of myself; for books, and agencies, and systems, are only remotely the instruments of my holy calling; my own spirit, soul, and body, are my nearest machinery for sacred service; my spiritual faculties, and my inner life, are my battle axe and weapons of war. M’Cheyne, writing to a ministerial friend, who was travelling with a view to perfecting himself in the German tongue, used language identical with our own:—” I know you will apply hard to German, but do not forget the culture of the inner man—I mean of the heart. How diligently the cavalry officer keeps his sabre clean and sharp; every stain he rubs off with the greatest care. Remember you are God’s sword, his instrument—I trust, a chosen vessel unto him to bear his name. In great measure, according to the purity and perfection of the instrument, will be the success. It is not great talents God blesses so much as likeness to Jesus. A holy minister is an awful weapon in the hand of God.”