This is a Swedish tune, with Latin words. It is a beautiful song, which dates from at least as far back as the 16th century (first published, as far as I know, in 1582). It would be most fitting for Christmastide, but since its name reminds us of the third week in Advent, and since that is only a couple weeks away, I will dare to post it now. (Yes, that excuse is a lot of nonsense. I just like the song, and feel particularly undisciplined today; plus, I fear I would forget to post it if I waited till Christmas.)
Oh yes, and I must say, the third stanza is especially noteworthy, for it shows that the traditional reading of the closed portal of the Temple in Ezekiel 44 in light of the Mary's ever-virginity is not mere classroom speculation, but part of the traditional piety of the Christian.