Why is resistor needed in ADC circuit
In my opinion, they can be removed because you will have to compare the voltage at non-inverting pin to the voltage at inverting pin anyway.

You have to have a voltage to compare with.

Figure 1. Apply 8 V to the Vref input and each of the comparators gets a proportional voltage.
In this case we've applied 8 V and there are seven steps so each comparator has a reference voltage between 1 and 7 volts.

So what's the point for having those resistors?

It's to generate the reference voltages.

Now if Vin &lt; 1 V all comparators will be off.
When 1 V ≤ Vin &lt; 2 V comparator 'a' will turn on.
When 2 V ≤ Vin &lt; 3 V comparators 'a' and 'b' will turn on.
etc.