Elstir, in his prime, does not paint beauty, but rather creates beauty from within himself and then paints it. He is blessed if his creation becomes incarnate. Take Gabrielle, his wife and favorite model. Marcel at first finds her rather plain, if imperious.
I understood then that to a certain ideal type illustrated by certain ideal lines, certain arabesques which reappeared incessantly throughout his work, to a certain canon of art, he had attributed a character that was almost divine, since he had dedicated all his time, all the mental effort of which he was capable, in a word his whole life, to the task of distinguishing those lines as clearly and of reproducing them as faithfully as possible. What such an ideal inspired in Elstir was indeed a cult so solemn, so exacting, that it never allowed him to be satisfied with what he had achieved; it was the most intimate part of himself; and so he had never been able to look at it with detachment, to extract emotion from it, until the day on which he encountered it, realised outside himself, in the body of a woman, the body of the woman who had in due course become Mme Elstir and in whom he had been able (as is possible only with something that is not oneself) to find it meritorious, moving, divine. How restful, moreover, to be able to place his lips upon that ideal Beauty which hitherto he had been obliged so laboriously to extract from within himself, and which now, mysteriously incarnate, offered itself to him in a series of communions, filled with saving grace. (II,586)
Marcel comes to understand the role of the mind as the creator of beauty.
When I understood this I could no longer look at Mme Elstir without a feeling of pleasure, and her body began to lose it heaviness, for I filled it with an idea, the idea that she was an immaterial creature, a portrait by Elstir. (II,588)
But the effort to look within takes its toll.
A day will come when, owing to the erosion of his brain, he will no longer have the strength, faced with those materials which his genius was want to use, to make the intellectual effort which alone can product his work, and yet will continue to seek them out, happy to near them because of the spiritual pleasure, the allurement to work, that they arouse in him; and, surround them besides with an aura of superstition as if they were superior to all things else, as if there dwelt in them already a great part of the work of art which they might be said to carry within them ready-made, he will confine himself to the company, to the adoration of his models….And thus the beauty of life, an expression somehow devoid of meaning, a stage this side of art at which I had seen Swann come to rest, was that also which, by a slackening of creative ardour, idolatry of the forms which had inspired it, a tendency to take the line of least resistance, must gradually undermine an Elstir’s progress. (II,588)