Against Addition

The Westminster Confession Chapter 1:6

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 in Scripture, or by good and necessary consequence may be deduced from Scripture:
   unto which nothing at any time is to be added, whether by new revelations 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.