This is one of the most perfect pieces of music that Vivaldi ever wrote. The text is half a verse from Psalm 69 (70) as a response to the versicle with which Vespers begins 'Deus in adjutorium meum intende'. It's one of a group of large-scale double choir works that Vivaldi wrote during the 1720s. It's a brilliantly antiphonal piece of music in which Vivaldi exploits the antiphonal potential of setting a double choir against the orchestra to the hilt. The second movement, an ecstatic Gloria in E minor is followed by a doxology in which the choirs unite in a fugue that have several subjects and counter-subjects. Enjoy :-).