Sentence:  This Introit is to be sung broadly, but always without heaviness, and almost in "half voice", without great nuances, and in a rather low tonality. It would give a serious <WSD>countersense</WSD> to sing it with a great cry of joy, and to give it "éclat" under the pretext that "it is Easter". 
Meaning of the word marked with <WSD> tags:  A nonsensical idea; a contradiction in terms; something that contradicts an established principle, architectural or musical style, etc.