Therefore the initial entry of the light and its subsequent turnabout and departure... Even when we do not know what results from a given phenomenon, on the strength of the above unshakeable premise we certainly know that it has some consequence, except that we have not understood it. Moreover, on the basis of that premise we can legitimately infer that the phenomenon in question is also necessary in order to produce a result of precisely the required nature.
To apply this to the subject under discussion: Since we see that the lights entered into the vessels and then turned back and went out, we infer that this must have happened for a reason. However, the reason cannot have been simply to produce the gradation (of the Partzufim) since that could have been brought about without this. We must therefore say that it was for some other reason. But since we see that this phenomenon comes to produce the gradation – for it is through this that it came about – we can therefore immediately infer that although the gradation could have been produced without this phenomenon, it must have required some condition that would not have been fulfilled had it not been produced in this way, as it goes on to say.