Dixit Dominus, a setting of Psalm 109 (or Psalm 110 in English versions) in B-flat major, written by Alessandro Scarlatti, is my favorite piece of choral music.
Probably written between 1718 and 1721, the psalm requires SATB chorus as well as soloists, and the typical baroque string chamber orchestra, but with a third violin part instead of a viola part. The vocal soloists sing arias as well as short solos embedded in all the choral sections, except for the tenor, who has no aria.
As in many baroque settings, the text is divided into fragments of one or two sentences, each fragment providing the basis for an aria or a choral movement.
1. Dixit Dominus. The opening movement is a choral number, with various appearances by all the soloists, with recurring use of "Dixit" as a sort of refrain. The overall feeling is one of assurance and stability.
2. Virgam virtutis. A supple aria for soprano, this movement, with its skips and arpeggios, recalls idiomatic writing for trumpet, which is in keeping with the military imagery of the words: "dominare in medio inimicorum tuorum," to dominate in the midst of thine enemies.
3. Tecum principium. In constrast to the previous movement, this haunting and gentle aria for alto is almost mystical. In it, God speaks to believers, saying that he was with them at the very beginning of their life.
4. Juravit Dominus. This movement is divided in two parts. In the first, the confident chorus returns (with the soloists) to express the inviolable nature of God's promises: "Juravit Dominus et non pœnitebit eum:" the Lord hath sworn and he will not repent. The chorus is especially insistent on the word non, repeating it forte in block chords. The second section, speaking of the priesthood of Melchisedech, is more flowing, and recalls the psalm-tone singing of the Middle Ages and the Renaissance, with the choral parts breaking off into melismae before the end.
5. Dominus a dextris tuis. In this aria, God's wrath is expressed by the bass voice and the low strings, all keeping a dotted-note rhythm. As in Handel's Messiah, God is represented at his most fearsome by the bass.
6. Judicavit in nationibus. The chorus sings again, beginning with a flowing voice-leading texture, breaking apart into contrapuntal 16th-note passages; all this multiplicity reflecting the the countless dead heathens, victims of the Lord's wrath. All parts come together as one in solid chords on "in terra," and break off again on "multorum." This is very subtle word-painting.
7. De torrente in via bibet. This is perhaps the most remarkable movement. A soprano/alto duet, the opening slow, almost languid descending lines reflect the image of drinking from the stream. The second part, with its crisp continuo and joyous ascending lines, extending into the upper range of both voices, portray both the literal and figurative associations of holding one's head up high: "exaltabit caput."
8. Gloria patri. The closing doxology isn't part of the psalm, but is a necessary part of its setting for liturgical use. All the stops are out, and instruments and voices manage to convey both urgency and inevitability in this impressive fugue. The final plagal cadence, with its beautiful ornamented suspensions (especially the 4-3 suspension in the tenor) complete the psalm, combining longing and its own satisfaction in one column of sound.
The only known period copy of this piece is a manuscript in Milan. The only recording I know of is by the English Concert.