Response to history.

"And behold a great red dragon, having seven heads, and ten horns, and having seven crowns upon his head. And his tail drew the third part of the stars of heaven, and did cast them to earth." (Rev 12:1-3 KJV)
"The Red Dragon and the Woman Clothed in Sun" by William Blake

Elements:

Line: Blake uses line here to contrast between the biblical red dragon of hell and the woman of heaven. He juxtaposes the dragon's harsh, bold line with the light flowing contours of angel. 

Color: The color of the piece is used to emphasize the difference between good and evil/heaven and hell. He uses the dark, muted colors for the red dragon, but brighter, more hopeful, golds for the woman. 

Shape: The dragon's form is so huge that it overpowers the whole piece. I'm not sure if the artist meant it this way, but looks as if the dragon is winning almost because he is so gargantuan in comparison to the other figure. 

Principles: 

Balance: I feel that the piece is pretty well balanced because the top portion is so dark, it seems not to take up as much of the overall space as the bottom half. 

Emphasis: Obviously, there is emphasis on the woman. She is the only true highlighted feature in the painting, unless you count the highlights on the back of the dragon. 

Contrast: I think I've already stated that he has contrasted the two figures. 

Btw, I didn't choose this for any particular religious reason. I just really like the Hannibal Lector movie, Red Dragon.