I hope my question does not break the rules. I can't understand how this statement can be true in the book which I've mentioned:

I cannot undestand why it's true because if I have two point charges with same sign and same magnitude then the electric field should be zero at point P:

But according to gauss's law it's not zero and it equal to electric field due to one of these point charges. So this electric field is only caused by the charge inside the closed surface, not the charges outside it!