The proposition consists of two parts. Part 1: Nothing is in vain. This explains how the lights entered into the vessels and afterwards turned back and went out. Part 2: And this is the individual root... This explains the reason for this phenomenon.
Part 1: Nothing is in vain. This is obvious from two sides. Firstly, that anything could be for no purpose is quite inconceivable in the Supreme Mind, for something that is without a purpose is quite unfitting and it is impossible that anything unfitting could exist in the Supreme Mind. Secondly, as we have already said, the Sefirot are the measures of all the creations in all their different parts and aspects as laid down in the Supreme Mind, and the Sefirot are nothing except this. If so, the Sefirot contain nothing that does not exist in the creations, and accordingly nothing is in vain.