As you can see here, imagine there is 100A current, there is a leakage current around 100mA go to your electrical equipment such as washing machine or television, and someone touches it (assume that human body resistance at the weakest which is 1,000 ohms), the 100mA will flow to you and you will probably die even though the RCCB has tripped, so when you have proper grounding/earthing such as 5 ohms, the leakage current will flow to the ground instead of your body. You will be safe.
