that ‘economy of salvation,’ ‘in which the rich, noble, righteous bridegroom Christ takes as spouse the poor, shamed, evil little whore.

An excellent excerpt from ‘Through the Son, Our Lord’: God as Mercy and Love in Martin Luther’s Theology   by Oswald Bayer  - 

“God action of salvation cannot be described in any other way; it use intense wording and takes place on the edge and the point of the rupture, as

‘[that] happy exchange, in which the rich, noble, righteous bridegroom Christ takes as spouse the poor, shamed, evil little whore[cf. Hosea 1-3] and acquits her of all evil, decorating her with all good things.  Thus it is not possible that the sins will damn her; now they lie upon Christ and have been swallowed up by him.  She thus has such a rich righteousness from her bridegroom that she can survive once again against all sins – even if they would lie upon her.  Paul speaks about this in 1 Corinthians 15:[57; 55; cf. Hosea 13:14]: “Praise and thanks to God, who has given us such a conquest in Christ Jesus, in which death is swallowed up, together with sin.”’ (WA 7:26.4-12;LW 31:352)

This passage cited from On the Freedom of a Christian is placed within a context in which Luther states three times what is meant by the unio (union) of the ‘Word of God’ and ‘soul,’ about God and the human being in faith.  …. that ‘happy transaction,’ and ‘economy of salvation,’ ‘in which the rich, noble, righteous bridegroom Christ takes as spouse the poor, shamed, evil little whore.’”

pp. 329-230