So long as baptism and the Supper are seen as “appendixes,” they will be seen as expendable. Characterizing baptism and the Supper as “appendixes” to the Word, further, is part and parcel of a Protestant tendency toward the “primacy of the intellect.” It is rationalism, in that it reduces baptism and the supper to a means for communicating information. But that is not what rituals are for. Treating baptism and the Supper as disguised sermons reduces them so they can be encompassed and tamed by Christianity.
-Peter Leithart, Against Christianity, 76-77.