DGR saw the original painting on his visit to Bruges in October 1849. The painting is the central panel of the so-called St. John's Triptych. It reconstructs the key spiritual event in the life of the Dominican tertiary and mystic St. Catherine of Siena (ca. 1347-1380), her so-called Spiritual Espousal to Christ. It took place in the late 1360s when she was taken up in vision into a music-filled Court of Heaven. Catherine was there given to Christ by the Blessed Virgin in the manner related in both DGR's sonnet and Memling's picture. Some accounts of the event have her surrounded by St. John (the Evangelist), St. Paul, St. Dominic, and the prophet David. In Memling's treatment, however, Catherine's influence is emphasized, a feature picked up by DGR, particularly in the sestet. The “damsel at her knees read[ing] after her” from the “spread book” comprises a figural form signifying a future that clearly includes the interests and ideas of DGR.

For the relation of the sonnet to DGR's aesthetic program see the commentary for .

The sonnet was composed at the time DGR saw the picture in October 1849. DGR's holograph for the 1850 printing is at Yale. Also extant is an interesting copy made posthumously by WMR. This is an important document because it preserves a set of revisions that represent DGR's later changes to the work. The autograph manuscript from which these revisions derive was certainly available to WMR when he was editing his brother's work for his first (1886) collected edition, because that text gives the revised version of the sonnet, not the 1850 version.

First printed in no.4 (1850) p.180 with a slightly different title as well as a few substantive variants from the 1886 text. DGR did not collect the sonnet in any of the editions published in his lifetime, but his brother brought it back into circulation in the 1886 collected edition's “Sonnets for Pictures” section, and it was collected thereafter.

Of the Memling painting that inspired the sonnet DGR wrote: “His greatest production is a large triptych in the Hospital of St. John. . . . I assure you that the perfection of character and even drawing, the astounding finish, the glory of colour, and above all the pure religious sentiment and ecstatic poetry of these works, is not to be conceived or even described” (letter to the PRB, 25 October 1849: I.84 ). DGR chose to try to make a description nonetheless, but in an equivalent imaginative form (a sonnet). DGR added: “I forgot to mention that Memling's pictures in the Hospital of St. John were presented to the Institution by that stunner in return for the care bestowed upon him when he was received here, severely wounded and in great want, after the battle of Nancy” ( I.85 ). The Hospital of St. John is now the Hans Memlingmuseum.