Another scene found in the late medieval collection of stories about saints, The Golden Legend, gives us another popular topic for painters, the Mystic Marriage. St. Catherine has a vision of some sort and has just been baptized by a priest, with the Virgin Mary as her godmother (that's a bit of long story on its own), and then the Virgin Mary says that she lacks nothing to be proper wife:
And so our Lady led her forth unto the quire door whereas she saw our Saviour Jesu Christ with a great multitude of angels, whose beauty is impossible to be thought or written of earthly creature, of whose sight this blessed virgin was I fulfilled with so great sweetness that it cannot be expressed. To whom our blessed Lady benignly said: Most sovereign honour, joy and glory be to you, King of bliss, my Lord, my God and my son, Lo! I have brought here unto your blessed presence your humble servant and ancille Katherine, which for your love hath refused all earthly things, and hath at my sending obeyed to come hither, hoping and trusting to receive that I promised to her. Then our Blessed Lord took up, his mother and said: Mother, that which pleaseth you, pleaseth me, and your desire is mine, for I desire that she be knit to me by marriage among all the virgins of the earth. And said to her Katherine, come hither to me. And as soon as she heard him name her name, so great a sweetness entered into her soul that she was all ravished, and therewith our Lord gave to her a new strength which passed nature, and said to her: Come my spouse, and give to me your hand. And there our Lord espoused her in joining himself to her by spiritual marriage, promising ever to keep her in all her life in this world, and after this life to reign perpetually in his bliss, and in token of this set a ring on her finger, which he commanded her to keep in remembrance of this, and said: Dread ye not, my dear spouse, I shall not depart from you, but always comfort and strengthen you. Then said this new spouse: O blessed Lord, I thank you with all mine heart of all your great mercies, beseeching you to make me digne and worthy to be thy servant and handmaid, and to please you whom my heart loveth and desireth above all things. And thus this glorious marriage was made, whereof all the celestial court joyed and sang this verse in heaven: Sponsus amat sponsam, salvator visitat illam, with so great melody that no heart may express ne think it.
The story is a literalization of the notion that the consecrated virgin is Spouse of Christ; but the Vision of Mystic Marriage is most closely associated with virgins who are martyrs or confessors, or who undergo extraordinary mortifications, since such women are especially united to the passion of Christ. In St. Catherine's case, of course, she was a martyr. Having such a vision is not a particularly uncommon religious experience, in fact -- there are literal dozens of cases in the calendar of saints, including a fairly well attested one by different St. Catherine, St. Catherine of Siena -- but the legend of St. Catherine of Alexandria seems to serve as the general template for the depiction of such things in art, and probably also for how the experience is interpreted.