Forgiveness and saving peace are repeatedly presented in Israel's Scriptures as gifts of God.
The other guests themselves ask, 'Who is this, who even forgives sins?' Luke thereby makes Jesus' identity the theological issue.
Jesus' unqualified pronouncement of forgiveness and salvation is strong evidence of his exercise of divine prerogatives.
The guests question Jesus' identity because he forgives sins.
Their question explicitly links Jesus' action to the larger issue of who he is.