It is not an amplifier, rather this is a latch or a Shmidt trigger. Think of it in the following way - you have Ve<Vin<Vc. Then you switch the power on. If we assume that initially the output of the opamp is @ 0v then the (+) input is at 0 as well. If Vin>0 the opamp output starts going down to Ve and the (+) input also follows through the divider which further drives the output down to Ve - so, positive feedback and the opamp saturates at Ve. The (+) inout gets a voltage that is defined by the divider between Ve and gnd. The same thing happens but in the oposite direction if initially Vin was <0. Now, if you start changing Vin, the opamp output will flip when Vin crosses the voltage at the middle tap of the divider. The values of the resistors are important only for setting this trigger points - they are two.