The languorous sound is given by the damper used by the arcs. You can really listen here to the majestic expressive capacity of Vivaldi in painting words with music (this is the psalm 126 normally performed during Vespers) . I find also amazing how the word "Somnum" (= latin for "sleep") is accompanied by a rocking rhythm and languorous sound, so expressive.....
"Cum dederit dilectis suis somnum:
ecce haereditas Domini, filii:
merces, fructus ventris."
But also the following is amazing:
here the lyrics in italian:
Se lento ancora il fulmine
cadra quell'empio, vittima
del giusto mio furor.
ritorna e ti perdono;
occhi versate in lacrime
tutto l'affanno d'un tradito amor."
Many years passed since I watched the last opera in my life (apart the ones I saw during my secondary school, I remember a wonderful Carmen in Turin). But I have never been really fond of it. I think it might be an interesting experience, now....