Ssu-ma Kuang's Comprehensive Mirror had a political mission. It's style and purpose was entirely to "utilize the history of the past to assist in governing." He collected 322 varieties of public and private works and drew from them historical lessons, then provided these to the emperor as apologues for the handling of national affairs.
而司馬光的《通鑑》則負有政治使命，其寫作風格與目的，全在「藉前人之史以資治」，他廣搜公私作品達三百廿二種，從中擷取歷史教訓，然後呈給皇帝，供作處理國事的鑑戒。