Ignoring R4 for the moment, its effect is negligible, I don't understand what its purpose is. 

The circuit is not functioning as a comparator. The closed loop circuit will attempt to balance the inputs of the opamp. It will adjust the voltage at V2 until the self-heating of the thermistor causes the thermistor resistance to be about 39 ohms.

Redrawing the circuit makes it easier to understand.


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![schematic](https://i.sstatic.net/ic3SK.png)

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