Mark Goodacre has brought up a good discussion on Mark 15:39 and the soldier's statement:
37. ὁ δὲ Ἰησοῦς ἀφεὶς φωνὴν μεγάλην ἐξέπνευσεν. 38. Καὶ τὸ καταπέτασμα τοῦ ναοῦ ἐσχίσθη εἰς δύο ἀπ' ἄνωθεν ἕως κάτω. 39 Ἰδὼν δὲ ὁ κεντυρίων ὁ παρεστηκὼς ἐξ ἐναντίας αὐτοῦ ὅτι οὕτως ἐξέπνευσεν εἶπεν, Ἀληθῶς οὗτος ὁ ἄνθρωπος υἱὸς θεοῦ ἦν.
Dr. Goodacre has asked the question: is this really a confession or is it a sarcastic remark on the soldier's part? His commenters have already noted several instances of ironic and sarcastic remarks throughout the passion narrative (as have I here). The question posed by some has been whether it's either sarcastic or confessional and I want to say that it's both.
If Mark is written as "Gospel" and these gospels were inherently liturgical from the get-go, then I think it has a double meaning. Irony only works in favor of the reader/hearer, not against them. It brings the reader closer to the author's/text's viewpoint, even if it's against the person who spoke the words. The readers/hearers have the 'inside scoop'. So, even if the soldier's remark is sarcastic, when the text was read aloud in the liturgy and heard by the people, they knew that "surely this man was (is) the son of God".