I like the comment about space. What I saw with lily's work was the drive to express the world that she saw. She constantly fights both the Tansley's in the world that tell her a woman can not paint and the practical Mr. Ramsay's that are always dulling the colors and defining the lines.
She does not see the scientific catagorized dull world. What this seems to point out to me with her(Woolf's) use of religious imagery is that Lily stands for the feminine side of spirituallity.
This looks like Woolf trying to show her own value to a world that did not see her or her work as of consequence. She shows that female strength (different from the masculine concept) and the female artist is not only of interest but of vital importance to the rounded growth of society. She shows a evolving world in the house that needs both the Tansleys and the Mr. Ramsays but also the Lily Briscoes and the Mrs. Ramsays as well as the Mintas and the Agustus Carmichaels.