Equipotential eliminates the possibility of current flowing at all across your body because it equalizes the potential by tying the phase, the neutral and the structure that you're on all together so that they are all at the same voltage rise, and that voltage rise is minimal.

Why equipotential zone must be bonded the best ground at the site?

Grounding makes sure that current will be directed along the ground or neutral wire in a system during a fault, but there is still the risk that if you touch the live wires, the current could travel through you into the ground instead of through the neutral line.

Why is grounding required?

Grounding helps protect you and your home from the dangers of damaged circuits or electrical overloads. When power surges happen, the excess electricity introduced to the system could leap out of the wiring. Without electrical grounding, this stray voltage could start a fire, damage appliances, or shock bystanders.