Part 1 of this work, which was originally meant to have a section called "Christmas games with the C
Part 1 of this work, which was originally meant to have a section called "Christmas games with the Christ child," opens with an allegro impetuoso whose polyphony was inspired by the composer's recent studies of Bach and features a notable trombone motif.  The "Eternal-Feminine" section of its 2nd part was admired when it premiered, and follows a section featuring Doctor Marianus while preceding an instrumental coda of the first part, a setting of the Latin hymn "Veni, creator spiritus." For 10 points, identify this work whose second part is a setting of the final scene of Faust, the eighth symphony by Mahler, nicknamed for the large number of musicians who performed it.
Part 1 of this work, which was originally meant to have a section called "Christmas games with the Christ child," opens with an allegro impetuoso whose polyphony was inspired by the composer's recent studies of Bach and features a notable trombone motif.  
Symphony of a Thousand [accept Mahler's Symphony Number 8 before mentioned]