When Mozart married his beloved wife, Constanze, against his father's wishes, he pledged to write a mass in her honor. He never finished it, and musicologists and historians continue to search for a reason why. What remains of his Great Mass in C Minor is a staggering work of improbable beauty, alternating choruses with arias performed by two male and two female voices. Maestro Masaaki Suzuki and four vocalists, Mozart specialists all, will scale the glorious heights of the Great Mass this weekend with St. Louis Symphony Orchestra and the St. Louis Symphony Choir. Performances are at 8 p.m. Saturday and 3 p.m. Sunday (November 9 and 10) at Powell Hall (718 North Grand Boulevard; www.slso.org). Tickets are $15 to $83.