The BSO website says that tonight's performance is sold out. Further info is available by following the links beginning on the page I've linked. I'm not sure how much of the popularity of tonight's performance is for the music, and how much has to do with Sir Colin, who has been pretty popular here. But a sellout is not a frequent occurrence.
This is a program not to be missed, IMO. As usual it will be streamed over WGBH (click Radio, then Listen WGBH 89.7) on Friday at 1:30 p.m. Eastern Daylight (Summer) Time (with a pre-concert show at 1:00), and over WCRB (click Listen Live) at 8:00 p.m. Eastern on Saturday. If you can listen to both, I especially recommend WGBH for the interviews that are part of the intermission and preview. But both give you the music.
I'm especially looking forward to the Berlioz piece. I don't think I've ever heard it, but his Requiem is spectacular and I'm hoping for something comparable musically. For me there is the added attraction that the text is a liturgical piece of thanksgiving to God. On Sundays outside Lent and Advent t is part of the Office of Readings (Matins). Great composers have composed settings in honor of victories or royal recoveries of health. M.-A. Charpentier and G. F. Handel come to mind as two who have contributed to the genre. Columbus is said to have ordered a Te Deum sung (probably on of the Gregorian chant settings) when his ships made land on his first voyage.
Check back for a review from the Boston Globe and maybe my own comments from the Thursday performance, which is part of my subscription — if I haven't already added them by the time you read this.