what does this circuit does?

If I'm not wrong, the highlighted part is a differential circuit. I found out that the voltage at point 1 is 4V and point 2 is 4V too. So what is the use of a differential circuit?

It amplifies the difference of the two signals on it's inputs and ignores signals that are common to both inputs.

The amplifier will not amplify noise common to both inputs unless the phases are different.

I've measured the voltages at both inputs, which are pin 9 and 10, 2V and 3V respectively. I am using 5V VCC by the way. So the difference between this 2 points is 1V. But how does it amplify the 1V to become 4V?