From the Belgic Confession (1561):
“We believe that those Holy Scriptures fully contain the will of God, and that whatsoever man ought to believe, unto salvation, is sufficiently taught therein. For, since the whole manner of worship, which God requires of us, is written in them at large, it is unlawful for any one, though an apostle, to teach otherwise than we are now taught in the Holy Scriptures: nay, though it were an angel from heaven, as the apostle Paul says. For, since it is forbidden, to add unto or take away anything from the word of God, it does thereby evidently appear, that the doctrine thereof is most perfect and complete in all respects. Neither do we consider of equal value any writing of men, however holy these men may have been, with those divine Scriptures, nor ought we to consider custom, or the great multitude, or antiquity, or succession of times and persons, or councils, decrees or statutes, as of equal value with the truth of God, for the truth is above all; for all men are of themselves liars, and more vain than vanity itself. Therefore, we reject with all our hearts, whatsoever does not agree with this infallible rule, which the apostles have taught us, saying, Try the spirits whether they are of God. Likewise, if there come any unto you; and bring not this doctrine, receive him not into your house.” (Article 7; emphasis mine–CD)
This particular article from the Belgic Confession highlights at least one reason why we have a Confession of Faith and a Heterodoxy Hall of Shame.