I love the contrast. Not even the light vs. dark, good vs. evil etc. but more specifically the dynamic vs. calm. As if the Living saint stands in the eye of the storm. Which is quite apt in this case.
St. Celestine the Living Saint, bringing the Emperor's Divine Justice to the forces of the Arch-enemy. And that is why you're one of my fav artists on DA, and my fave DA 40k artist EVER! EMPEROR BLESS YOU MA'AM!!
At the risk of info-bombing.... St. Celestine, the angelic greater 'warp entity' of the God-Emperor, about to unload righteous fury on the demonettes of Slaanesh. She's technically a "greater demon" (sorry for the quotes) and it gets confusing in 40k for the non-fanboys, but the TLDR version is this: the Emperor was a man, now he's a god, or god-like, and he and his forces (including warp entities,) lower case demons, fight the forces of Chaos led by the Ruinous Powers (whose forces include more traditional looking demons, as well as mortals pledged to their cause). The Armies of the Emperor include Space Marines (genetically engineered, post-human killing machine super-soldiers that make master chief from halo look like a pansy) the Imperial Guard (think modern US Military) and the Sisters of Battle. (female warrior paladins) that fight in power armor, but aren't genetically engineered like Space Marines. St. Celestine, the subject of this image, is one of the Emperor's champions, and keeps getting brought back to life upon death so that she might continue to slay the servants of evil and bring hope to the Imperium. (she also used to be a Sister of Battle)
Warhammer 40k is essentially dystopian science fantasy, and it can be overwhelming at first for the unfamiliar, so don't let it inimitable you. I've been involved in it now for almost 2/3 rds of my life, and I love it.
If you want to learn more, I recommend ArchWarhammer on youtube. He has a series of intro videos that help set the stage.