I got this from John Bevere's Bait of Satan curriculum and thought it was pretty good.
A slave: has to.
A servant: gets to.
A slave: does the required minimum.
A servant: does the maximum potential.
A slave: forced to go 1 mile.
A servant: choses to go 2 miles.
A slave: feels robbed.
A servant: gives freely.
A slave: fights for his rights.
A servant: lays down his rights for the sake of others.