I was told by our editor, “You must go hear Blue Heron.” Silly me, I hadn’t yet heard them — and there is no excuse for that. I agreed to review this concert in part to rectify my oversight, although I may be the only person who views writing a concert review as something akin to an act of contrition. (And I never was a Roman Catholic.) But last night’s standing-room-only concert at Boston College’s Gasson Hall proved to me just how enormous was my oversight in not having heard Blue Heron perform before. Now I can tell you, “Go. You must hear Blue Heron.” This was a thrilling, soaring, quasi-religious experience. You have three more opportunities to hear this program; stop reading now and get yourself to a venue.

The program opened with Ave fuit prima salus of John Mason (c. 1480 – 1548). Taking as its text words attributed to Jacopone da Todi, a 13th-century Franciscan, this 20-minute work is a gloss, an expansion, a veritable compendium of harmonies in praise of the Virgin Mary, as each succeeding verse begins with the following word from the prayer “Ave Maria.” It is also an opportunity to hear something like the compositional genius of John Mason. We know very little about this ubiquitously-named composer (making it very hard to separate fact from fiction, this John …, this Mason …, from any number of others). We also only have three of the five partbooks from the Peterhouse collection, so what we heard is reconstruction by Nick Sandon based on the surviving three partbooks and the musical conventions of the time. In this, the shorter work on the program, already Blue Heron’s strengths were obvious. This small ensemble, with two or three singers per part, has a beautiful grasp of vocal blending, a tight coherence as an ensemble, and good enunciation. Under Scott Metcalfe’s clear direction, Blue Heron vocalized the agony and the ecstasy embedded in the mystery of Mary and set to music by Mason.

There followed a brief pause; while the singers rested their voices, Metcalfe set up the rest of the concert: Missa Inclina cor meum, a complete Mass Ordinary by Nicholas Ludford (c. 1490 – 1557) — again music surviving in the Peterhouse partbooks and now restored by Sandon. This mass is based on a simple (“unpromising” is Metcalfe’s term) cantus firmus that does not associate this Mass with any particular festal occasion. For that reason, Blue Heron prefaced it with a troped Sarum Plainchant Kyrie – the Kyrie Cunctipotens genitor. It is a fascinating work, both theologically (with its expansion and variation of the standard “Kyrie eleison” text) and musically. Then Ludford’s Missa, with its “meandering, musing” music (again, Metcalfe’s terms). I cannot help wondering if Ludford composed this Mass as a challenge, either one he set himself or a dare set by another: can you make distinctive music out of a seemingly unremarkable cantus firmus? Ludford certainly did.

There is soaring beauty, beginning with the opening Gloria. There is a wealth of moods, from jubilant elation to hauntingly abject remonstrations. The Credo alone ranges from proud declamation through profound, indeed mysterious, interiority, to optimistic hope. Ludford’s polyphony, with its grounded and drawn-out bass line, treble arabesques, and solid yet never stolid middle voices, effectively captures the weight of the words.

I found the tempos Metcalfe chose to be well suited to the music. The enunciation of the singers made the text easy to follow. Gasson Hall is a lofty, vaulted space, but audience and ensemble were arranged quite close together on ground level. Because of the space and layout, some sibilants were more pronounced than intended; this constant problem when singing posed the only challenge to the otherwise impeccable ensemble singing of Blue Heron. I did hear variability in the Latin pronunciation — hard and soft “g”s in virgine; both “t” and “ts” in Pontio. Others less schooled in Latin might not have noticed, but I admit to being surprised when I heard it. The variation in pronunciation was not jarring, but I found it worth remarking. These are, though, nugae compared to the 60-odd minutes of gorgeous polyphony which Blue Heron provided for the delectation and edification of all assembled.

This concert repeats tonight at 8 pm in St. Cecilia Parish (18 Belvedere Street, Boston), Saturday at 8 pm in First Church in Cambridge, Congregational, and Sunday at 4 pm in St. Ignatius of Antioch Episcopal Church (87^th Street & West End Avenue, New York). As at the beginning, so at the end: “Go. You must hear Blue Heron.”

Cashman Kerr Prince is trained in Classics and Comparative Literature and is now a Visiting Scholar in the Department of Classical Studies at Wellesley College.  He is also a cellist of some accomplishment, currently playing with the Brookline Symphony Orchestra.