The reason that Scripture is the sole authority for all matters of faith and practice is that only scripture is Θεο πνευστὁς (God-breathed). The human authors of scripture wrote as moved and inspired by the Holy Spirit, and only those written words inspired by the Holy Spirit are considered as part of the written revelation of God. The last human authors of the New Testament, having fulfilled their ministry and gone on to glory, have not been replaced, either in whole or in part, and thus, there is no more authoritative word of God to be given unto men other than what has already been given. It has not been given to any single office within the Church to interpret Scripture or bind the conscience of believers to follow human proclamation. This is the error of Rome which has vested authority in the church itself, through the papacy, to bind both practice and conscience in violation of scripture itself. While not inspired words, the framers of the 1689 Second London Baptist Confession of Faith penned words that should serve to encourage all true believers in the Lord Jesus Christ:
1.1 The Holy Scripture is the only sufficient, certain, and infallible rule of all saving knowledge, faith, and obedience, although the light of nature, and the works of creation and providence do so far manifest the goodness, wisdom, and power of God, as to leave men inexcusable; yet are they not sufficient to give that knowledge of God and his will which is necessary unto salvation. Therefore it pleased the Lord at sundry times and in divers manners to reveal himself, and to declare that his will unto his church; and afterward for the better preserving and propagating of the truth, and for the more sure establishment and comfort of the church against the corruption of the flesh, and the malice of Satan, and of the world, to commit the same wholly unto writing; which maketh the Holy Scriptures to be most necessary, those former ways of God's revealing his will unto his people being now ceased.
1.4 The authority of the Holy Scripture, for which it ought to be believed, dependeth not upon the testimony of any man or church, but wholly upon God (who is truth itself), the author thereof; therefore it is to be received because it is the Word of God.
1.6 The whole counsel of God concerning all things necessary for his own glory, man's salvation, faith and life, is either expressly set down or necessarily contained in the Holy Scripture: unto which nothing at any time is to be added, whether by new revelation of the Spirit, or traditions of men. Nevertheless, we acknowledge the inward illumination of the Spirit of God to be necessary for the saving understanding of such things as are revealed in the Word, and that there are some circumstances concerning the worship of God, and government of the church, common to human actions and societies, which are to be ordered by the light of nature and Christian prudence, according to the general rules of the Word, which are always to be observed.
1.9 The infallible rule of interpretation of Scripture is the Scripture itself; and therefore when there is a question about the true and full sense of any Scripture (which is not manifold, but one), it must be searched by other places that speak more clearly.
1.10 The supreme judge, by which all controversies of religion are to be determined, and all decrees of councils, opinions of ancient writers, doctrines of men, and private spirits, are to be examined, and in whose sentence we are to rest, can be no other but the Holy Scripture delivered by the Spirit, into which Scripture so delivered, our faith is finally resolved.
