I. Look at the remarkable combination of revelation and truth, and conscience which the text exhibits. The Apostle knew nothing or cared nothing for those controversies between revelation and conscience, or faith and conscience, or authority and conscience which now agitate men's minds. As these several things presented themselves to his mind there were no rival claims to be adjusted between them. Is Christian doctrine to be accepted because it is a Divine revelation of the evidence of which faith is to judge? or is it to be accepted because, and only as far as it commends itself to the human conscience? Modern writers have a great deal to say on this question. St. Paul had simply nothing nothing, at least, that he thought it necessary to say. Faith, and a pure conscience with him went hand in hand. Both were necessary, and there was no need to decide the limits of their respective domains. He had united them together in his direct charge to Timothy himself. He now unites them again in stating his qualifications for the first step in the ministry. A good conscience is the natural element in which a sound faith exists. Therefore, the man who deliberately thrusts away from him the former, renders himself incapable of holding the latter, or at least places himself in great danger of making shipwreck of it. A true faith cannot live in an impure heart, though it may be there dormant and inactive. Indulgence in sin, which obscures the lesser light of man's moral nature, must at length hide out the view of God Himself, though we have the promise of our Lord that the pure in heart shall eventually see God, and from which we may infer that it is darkness and sin alone that can entirely obscure Him. Yet we cannot doubt the fact that purity of outward life may co-exist with unbelief. It does not, however, by any means necessarily follow that purity of outward life involves that purity of heart to which our Lord's promise is attached. With regard to it, the teaching of the New Testament is no way doubtful. The power within man which triumphs over the strength of his natural corruption is the power of faith, faith in Christ as an ever-living Redeemer, and that faith is an instrument in the hands of the Holy Spirit, by which He works upon the hearts of men. It is thus alone, according to the teaching of the New Testament, that true purity of heart can be attained so far as man in his present state is capable of attaining it.
II. The idea which any man forms of the evil of sin, must depend upon the purity of his conscience; and it therefore follows that purity of conscience is an important element in determining our belief upon such doctrines as the Incarnation and the Atonement, or to use the words of the text, that those parts of the mystery of faith must be held in a pure conscience. And the same may be said of any conception of God which includes the idea of holiness as a part of His character. It is true that all our ideas of holiness are relative and imperfect, as are the teachings of conscience itself; but what idea of beauty, and excellence, and holiness, can be formed by one whose own heart and conscience are defiled, or how can such an one form any conception of the holiness of Him who is of purer eyes than to behold iniquity. The mystery of that faith whose seat is in the heart and conscience cannot abide in an impure dwelling-place. From the polluted sanctuary are heard the ominous words the cry of a lost faith: "Let us depart hence."
J. H. Jellett, Oxford and Cambridge Journal,June 7th, 1877.
Reference: 1 Timothy 3:9. Homilist,3rd series, vol. vi., p. 6.1.