If the flow of current remains intact in a circuit , then what are resistors for

Resistors have 2 basic uses.

1. To convert energy to heat/light (e.g. a light bulb is a sort of resistor)

2. To provide a required voltage; e.g in an electronic devices (TVs, computers, etc), resistors ensure the correct voltages are applied to other components.

No thats not true, current is the number of charges passing at a point per second. These charges have a certain amount of energy. Resistors use up some of the ENERGY but the number of charges passing the point (the current) remains intact.

If you actually had 0 resistance, then you could not have current flow as you could not create a potential difference. Thus resistance is necessary for current flow.

Resistors lower voltage, through dissipation of energy in the form of heat.

Resistors change the current flow