Reverse voltage protection: what is the function of C8 in this schematic?
R2 and the zener are there to protect the MOSFET gate from the input voltage exceeding the gate voltage rating. Even a momentary transient can permanently damage the thin gate oxide layer.

The capacitor is there to ensure the MOSFET switches rapidly and does not linger partially on dissipating excessive power. Otherwise the gate charge has to be supplied through the resistor, and the Miller effect results in a relatively long turn-on time especially for a large low-Rds(on) MOSFET.