"And the glory of the Lord" is the first time the entire chorus is heard in performances of "The Messiah." After the prelude and first three movements featuring soloists, this first hearing of the full chorus is a glorious introduction to the full sound of all the singers who have assembled for the performance.
The piece is written in the key of A major, which Handel considered to be the most cheerful of all possible key signatures. The allegro speed marking keeps the interplay of melody among the four vocal parts moving. Handel considered melismas, the rapid series of notes sung on a single syllable, to be a joyous sound and used them extensively in many movements of "The Messiah," including "And the glory of the Lord." Chord progressions are predictable - there are no harmonic moments of discord in the chorus. The melody line soars to the heights of God's glory, taking singers, instrumentalists, and listeners along with it.