This weekend debuts of a major new choral arrangement and of a bigger and better organ will be made during the 11 am “Messiah Sunday” Mass at Blessed Mother Teresa (BMT) Parish, marking 16 years that Music Director Sheldon Lee has been recreating a grand European Advent tradition in Dorchester parishes.

A full orchestra and augmented choir will perform classical religious selections throughout the regular ceremony: a worship service and free concert all in one. Since this is the best-attended service of the year at St. Margaret Church, regulars come as much as an hour early to secure a seat.

“There’s no parish in the Boston archdiocese that does anything as ambitious as this during Advent,” observes Lee, who received his Masters in Voice from New England Conservatory.

Lee is world-premiering his own choral arrangement of selections from Richard Wagner’s opera Tannhauser, including the famous “Pilgrim’s Chorus,” to which he has added his own pilgrim-themed English language lyrics. Members of the Boston Wagner Society will attend this premiere.

Other classical selections performed will include, as the recessional, “The Hallelujah Chorus” from Handel’s Messiah, the ubiquitous holiday favorite that lends its name to the program. Add to that compositions by Haydn, Orff, Coulais, and Fauré performed by the augmented BMT choir and backed by 30 professional musicians from orchestras all over New England.

Many of these guest musicians are brass-players, but this Messiah Sunday will also mark the debut of a just-installed Rodgers Allegiant organ, featuring 51 internal orchestral voices and 184 stops, equivalent to 241 pipe ranks.  Though this instrument is two years old, it replaces an much older organ, originally installed in St. Ambrose’s chapel, then moved to St. William’s, and moved again to St. Margaret’s when the latter two parishes merged into Blessed Mother Teresa.  

Lee got the Messiah Sunday idea from the great masses composed by immortals like Handel, Mozart and Shubert, as well as from having attended services in Austria where this type of music-packed mass is celebrated every week.

Fierce loyalty to this tradition and to Lee himself explains why the unpaid choristers (about 70 percent of whom have been with Lee since his Savin Hill days) collect thousands of dollars every year to underwrite this production, defraying about 40 percent of the expenses.

Veteran choir member Jane Drinkwater, a former Boston Public School psychologist, explains her strategy.

“I invite family and friends to Messiah Sunday and the Easter liturgy so they can get a sense how the music praises and is in itself a prayer,” she said. “Then I hit them up for money.”

Drinkwater regrets that two of her regular contributors have lost their jobs this year and don’t have much disposable income.  She encourages all sacred music-lovers to send checks made out to Blessed Mother Teresa Parish (800 Columbia Road, Dorchester, 02125), earmarking their donations either for the expenses of Messiah Sunday or for the organ fund.

BMT plans a free formal organ dedication on January 16th at 3p.m., featuring 4 to 6 prominent Boston area organists and a reception. For further information or to make a contribution, call 617 513-8254.