Ary Sheffer's painting shows the two saints in that ecstasy St. Augustine describes in the tenth chapter of book nine in the Confessions:
23. As the day now approached on which she was to depart this life -- a day which thou knewest, but which we did not -- it happened (though I believe it was by thy secret ways arranged) that she and I stood alone, leaning in a certain window from which the garden of the house we occupied at Ostia could be seen. Here in this place, removed from the crowd, we were resting ourselves for the voyage after the fatigues of a long journey.
We were conversing alone very pleasantly and "forgetting those things which are past, and reaching forward toward those things which are future." We were in the present -- and in the presence of Truth (which thou art) -- discussing together what is the nature of the eternal life of the saints: which eye has not seen, nor ear heard, neither has entered into the heart of man. We opened wide the mouth of our heart, thirsting for those supernal streams of thy fountain, "the fountain of life" which is with thee, that we might be sprinkled with its waters according to our capacity and might in some measure weigh the truth of so profound a mystery.
24. And when our conversation had brought us to the point where the very highest of physical sense and the most intense illumination of physical light seemed, in comparison with the sweetness of that life to come, not worthy of comparison, nor even of mention, we lifted ourselves with a more ardent love toward the Selfsame, and we gradually passed through all the levels of bodily objects, and even through the heaven itself, where the sun and moon and stars shine on the earth. Indeed, we soared higher yet by an inner musing, speaking and marveling at thy works.
And we came at last to our own minds and went beyond them, that we might climb as high as that region of unfailing plenty where thou feedest Israel forever with the food of truth, where life is that Wisdom by whom all things are made, both which have been and which are to be. Wisdom is not made, but is as she has been and forever shall be; for "to have been" and "to be hereafter" do not apply to her, but only "to be," because she is eternal and "to have been" and "to be hereafter" are not eternal.
And while we were thus speaking and straining after her, we just barely touched her with the whole effort of our hearts. Then with a sigh, leaving the first fruits of the Spirit bound to that ecstasy, we returned to the sounds of our own tongue, where the spoken word had both beginning and end. But what is like to thy Word, our Lord, who remaineth in himself without becoming old, and "makes all things new"?
According to this site, the Pre-Raphaelite Brotherhood took some interest in Scheffer's works:
Of Protestant Dutch origin, the French painter came to Paris in 1811. He was to have a brilliant career as the drawing teacher of King Louis-Philippe’s children.
When he arrived in Paris he joined Pierre Guérin’s (1774-1833) workshop. He proved very gifted and was able to work in different fields, such as landscapes painted “sur le motif” (from nature), historical scenes in the Romantic style, religious subjects, for which he is very well-known : “Saint-Augustine with his mother, Saint Monica”. He made many copies of this in 1849 and 1855. . .
. . . After being much esteemed by the British Pre-Raphaelites, he sank into obscurity but nowadays is considered a major player in the Romantic movement. . . .
I can see how his subject matter, paintings that depict scenes from Dante's Divine Comedy and Goethe's Faust, the religious images of King St. Louis, etc., would have attracted the Pre-Raphaelite Brotherhood. But his style, so classical and more like Ingres, would not have appealed to them.