Reason for having a resistor at gate of MOSFET
As mosfets have maximum gate voltage rating, the resistor divider at gate is used to lower the voltage the gate sees for cases when full voltage cannot be applied to it.

For example, IRF3205 has Vds rating of 55V, but Vgs - only 20V. If your circuit is operating at 50V, you can't apply 50V to gate, you need to lower it, for example by means of resistor divider on the gate.