Lyric discussion by k33nbl4de 

Cover art for Black Winter Day lyrics by Amorphis

From the language used (almost identical to the Kalevala translation I've read), this is translated from the monologue of Louhi's daughter after being reminded of how her life will change with her marriage to Ilmarinen. This is close enough that there's pretty much no doubt.

Song Meaning

Just giving the exact quote (from the W.F. Kirby translation of the Kalevala, about 100 years old so the language is dated, and imitating the unusual metre of the original Finnish text so possibly slightly rearranged) I'm going to put it against the individual lines of the song to show the similarity, all the lines kept in the order they're in in the Kalevala.

Kalevala: "Such the feelings of the blessed, Such the thinking of the happy" Song: "This is how the lucky feel, How the blessed think"

K: "As the spring day at its dawning" S:...