http://www.ccel.org/ccel/mcgarvey/gospels.vii.xi.html
24 No man can serve two masters: for either he will hate the one, and love the other; or else he will hold to the one, and despise the other. Ye cannot serve God and mammon.
The two masters here are God and mammon. What is mammon? It was a common term to represent wealth. Jesus is personifying “wealth”, or perhaps the pursuit of wealth, as a master. How do you serve this idea, this inanimate object? Really, the pursuit of wealth is the pursuit of self. In the same way that an athlete sets a goal for himself – “to run a marathon”, and then devotes all of his energy to accomplishing the goal, the master isn’t the marathon, it is the athlete. That’s why we call it “self-discipline”. To pursue wealth is to set a goal and then pursue it. So the two masters in this sentence are really “God” and “self”.