Why should we intercede for others?

Prayer is like advertising in the newspapers. 

You make known your wants to those in the spirit world who take a pleasure in responding to requests of the kind you put forth—these spirits have means of knowledge on the subjects that you pray for and so they respond to the call more readily. As they obtain relief and happiness in their sufferings by rendering that aid to others, which they are best qualified to give, they respond readily to prayers for help in that direction.