Here's my take on it:
R4 and R1 form a voltage divider, but with a ratio of 0.99 it won't have much effect on the input. Maybe R1 is just there so that the left end of C3 isn't left floating at DC.
C3 and R2 form a high-pass filter, with a cutoff frequency of about 0.05Hz if I've done the maths right.
The op-amp is configured as a non-inverting amplifier with a gain determined by R3, C2 and R5. At DC, C2 is an open circuit, so it functions as a voltage follower with unity gain. At higher frequencies, the gain rises. At 50Hz it will be about 100, and it will approach a maximum of about 200 somewhere above 500Hz. This curve is probably chosen to compensate for the characteristics of the microphone.
You haven't shown values for C1 and C4; I'm assuming they're something small. At very high frequencies, probably well above audio, C4 will shunt the input to ground and C1 will short the inputs of the op-amp together, reducing its gain to zero. This will be to prevent the circuit from becoming unstable and oscillating at high frequency.
I'm guessing the ganged pot is a panning control, so you can set where the mic sound appears to come from between the left and right channels. If that's the case, it will be wired so that the two pots move in opposite ways, i.e. when one wiper moves towards the op-amp output, the other moves away from it.