Meaning and function of "以" in "子路，人告之以有过，则喜"?
以 functions as 'with' here


子路 (a student of Confucius)

人告之 - people inform him

以 - with (the information of) 

有过 - (he had) made mistake，

则喜 - be happy (when they do) 

When people pointed out 子路's mistakes, he would feel happy (we can presume he was happy to hear about his mistake so that he can make amends)

"闻过则喜" (happy when hear one's own mistake) is a sign of a wise and moral man

In real life, most people would 闻过则怒 (get angry when he was told he made mistake)