Et sepultus resurrexit; certum est, quia impossibile est."
It is almost impossible, without asceticism of a radically inartistic kind, to treat with the resources of instrumental music and free harmony such passages as that from the Crucifixus to the Resurrexit, without an emotional contrast which inevitably throws any natural treatment of the Sanctus into the background, and makes the A gnus Dei an inadequate conclusion to the musical scheme.
Bach contrives to give this anti-climax a definite artistic value; all the more from the fact that his Crucifixus and Resurrexit, and the contrast between them, are among the most sublime and directly impressive things in all music. To the end of his Resurrexit chorus he appends an orchestral ritornello, summing up the material of the chorus in the most formal possible way, and thereby utterly destroying all sense of finality as a member of a large group, while at the same time not in the least impairing the force and contrast of the whole - that contrast having ineffaceably asserted itself at the moment when it occurred.
This gives the utmost possible effect of finality to the whole Credo, and contrasts admirably with the coldly formal instrumental end of the Resurrexit three movements further back.