A differential amplifier amplifies the difference between the two input voltages but suppresses any voltage common to the two inputs. Based on this scheme

[![enter image description here](https://i.stack.imgur.com/AVz32.png)](https://i.stack.imgur.com/AVz32.png)

the differential amplifier is substracting an input with a delayed input and outputing a tiny difference to the integrator and that is confusing. So as mentioned in the title, how does the differential amplifier behave or whats is its role here?

**Note**: am a beginner fascinated by electronics, bear with me.