Why jeep(four wheel drive) is best for mountain ride?

Four wheel drive means engine power is supplied to all four wheels.Most of our vehicles working either on front wheel or rear wheel drive.We take an example of bike to explain the scenario,in case of bike engine power is supplied to back wheels through chain.There is no power supplied to front wheel bike running with the power of back wheel. This is called rear wheel drive.
Mountain ride and slippery roads four wheel is preferred because two wheel drive will not able to control.Below is the layout of four wheel drive.

Jeep is build in the concept of four wheel drive,power is given to all four wheels. This is controllable we can change to normal when we want. When we drive in mountain since power is applied in all the wheels it can claim easily.
Generally four wheel drive is applied to heavy vehicles and mostly used in army.