"'There
was matrimony in Paradise, and yet there was no carnal intercourse.
Therefore carnal intercourse is not an integral part of matrimony' (In IV Sent. d. 26, q. 2, a. 4, sed c. 1; Summa theol.,
Supplementum, q. 42, a. 4, sed c. 1). According to Aquinas, it is
wrong [(ne faut pas)] to take from [Gen 1:27] and similar texts the
liberty of affirming that sexuality—masculinity and femininity—enters
into what constitutes man in the image of God. Such an idea is contrary
to the very notion of theology according to Aquinas, which consists in
bringing to bear upon both creation and man the very regard of God, [and
doing so] from God, namely from revelation and the gift of faith. By
contrast, the idea of seeing in masculinity and femininity an element of
the image of God in man comes from [1] bringing an exclusively human
regard to bear on the human being and from [2] the confusion between the
essence of man and his activity. Thomas grounds the imago Dei in
the spiritual nature of man, [in] the intelligence and the will [that]
constitute him as man. For in God there is an intelligence and a will,
but not a body: 'God is spirit'. . . . Moreover,
the-image-of-God-that-man-is is an image to be perfected by virtuous and
meritorious activity. It is by his activity that man 'becomes' the
image of God, and this means that [(et en cela)] the exercise of
sexuality, as well as [that] of perfect continence, realizes this
image. Were masculinity and femininity to constitute for man an element
of his being in the image of God, [then,] on the one hand, God would
have to have a body, for the divine ideas of masculinity and femininity
are not principle[s] of 'being in the image of,' for they are ideas, as
Augustine put it so very well: 'it is there where there is no sex that
man was made to the image of God, that is in the spirit of his mind' (De Trinitate XII.3.12).
[And,] on the other hand, all would have to exercise [their] sexuality
in order to perfect this image, with the absurd consequence that those
who live in perfect continence would never realize it."
Adriano Oliva, O.P., "Essence et finalité du marriage selon Thomas d'Aquin pour un soin pastoral renouvelé," Revue des sciences philosophiques et théologiques 98, no. 4 (2014): 604n11 (601-668), translation mine.