This poem has a literal side and mythical side to it meaning. The literal side would just be that it is about two sisters with different aspects. The mythical side could be referring to the two sides of Persephone to show the connections between "shade and light".
In the first stanza, it introduces the two sisters, different as dark and light. One sister is very happy while the other is awfully depressed.
In the second, third, and last stanza, it talks about the aspects of the sister of the shade side. This sister is a logical, mathematical, and thinker sort of person. She spends her time dark shadowy room on her mechanical machine. As she is working on the mechanical machine, she is marking her time. I interpreted the lines "At this barren enterprise Rat-shrewd go to her squint eyes, Root-pale her meager frame." as the writer saying that as she is doing her boring job she never goes outside into the world, she become white-skinned.
She also becomes skinny because the lack of food that she gets inside her room. This sister goes to her grave having bitter life and as a virgin as said in line 26 and 27. "Worm-husbanded, yet no woman", to me means that she was having some "problem" with her sex life.
In the fourth, fifth, and sixth stanza, it talks about the aspect of the sister of the light side. In this few stanzas, the speaker is pictured in a very happier place. This other sister is a vibrant, nature-connected woman whose surroundings clearly show that she has a happy life. "Bronzed as earth, the second lies, Hearing ticks blown gold Like pollen on bright air." to me I interpreted as the writer saying that she is always out with nature that she...