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differential amplifier in delta sigma converter

A differential amplifier amplifies the difference between the two input voltages but suppresses any voltage common to the two inputs
VO = Ad (V1 - V2) **(ideal differential amplifier)**.
The differential Gain (Ad = – (R3 / R1))
CMRR = 20 logs (Ad / Ac)
![differencial amplifier](https://electrical.codidact.com/uploads/NBSzVcJ6Xt1DuYmKtCG5RdNT)
so as an example: V1=5.005 V2=4.995 Ad=100 **(ideal opamp)**
VO = Ad(V1 - V2)
VO = 100(5.005-4.995)
VO = 1 volt
so now the questions:
~~1. why we need only the difference?~~
~~2. in the delta-sigma converter why we are substracting an input with an delayed input?~~
~~3. why we need a differential amplifier in the delta-sigma converter?~~
~~Note: am a beginner fascinated by electronics I did a lot of reading before I post my questions here so if my questions look a little stupid bear with me and guide me that gonna be nice of you.~~

A differential amplifier amplifies the difference between the two input voltages but suppresses any voltage common to the two inputs
VO = Ad (V1 - V2) **(ideal differential amplifier)**.
The differential Gain (Ad = – (R3 / R1))
CMRR = 20 logs (Ad / Ac)
![differencial amplifier](https://electrical.codidact.com/uploads/NBSzVcJ6Xt1DuYmKtCG5RdNT)
so as an example: V1=5.005 V2=4.995 Ad=100 **(ideal opamp)**
VO = Ad(V1 - V2)
VO = 100(5.005-4.995)
VO = 1 volt
Now the questions:
1. why do we need only the difference?
2. in the delta-sigma converter, why substracting an input with a delayed input?
3. why do we need a differential amplifier in the delta-sigma converter?
Note: am a beginner fascinated by electronics. I did a lot of reading before I post my questions here so if my questions look a little stupid bear with me and guide me that gonna be nice of you.