David was a supporter of the Revolution and of Marat whose death he made famous in the following painting. Notice how Marat is painted in the style of the dead Christ or a martyred saint. In no time at all Marat would be so celebrated as a symbol of the Revolution that thinking of him in sacred terms would become almost normal.
The following is a very nice slide show of some of David's paintings. This is a good introduction to his vast output of mythological and historical paintings and his portraits.