פירוש על ברכות 105:7

[THE SAGES ISSUED A] DECREE BECAUSE OF THE FIRST GENTILE, AND THE FIRST GENTILE BECAUSE OF THE FIRST PILLAR [OF FLAME]. There is a general principle that when our Sages legislate decrees that are designed to protect us from violating a prohibition, they do not enact a second decree to protect us from violating the first decree. It seems that in the instance we are discussing here, we have this situation. The initial fear is that one might recite the b’rochoh on the first pillar of light that comes from the gentile’s fire. We therefore say that you cannot recite a b’rochoh on a gentile’s fire at all. That is one decree. We are now extending that to include a second gentile. This seems to be a decree to safeguard us from violating a previous decree.
This is one decree, which our sages decreed, that any fire that is in the hand of a gentile cannot be used for the b’rochoh, even though it is somewhat of an expansion of the original fear that one may recite a b’rochoh on the very first pillar of light, the sages sometimes do expand the initial decree to include a second level because if not for this second level of the decree that includes any fire in the hand of a gentile this first level of the decree, would not remain in practice. Our Sages understood that when the decree would be passed on to the regular populace, they would not understand that there is an essential difference between a first gentile and a second gentile. If the fire of a second gentile is permitted for the recital of a b’rochoh, they would not understand why the fire of the first gentile is forbidden. They therefore legislated that any fire of a gentile may not be used for the recital of the b’rochoh. All facets of this decree, the first and second gentile’s falls into the context of one decree. Any further legislation to protect one from violating this first expanded decree, for example prohibiting a fire lit by a Jew from a gentile’s fire, would be a decree for a decree, which our Sages did not do.
However, upon a fire that a gentile kindled from a Jew’s fire and upon a fire that Jew kindled from a gentile’s fire we may recite a b’rochoh, and that is how we rule. Extending the decree beyond a gentile’s fire to include a fire that a Jew lit from a gentile’s fire or vice versa would be a decree to protect us from violating a decree, which our Sages did not do.

Who may have kindled his light on the Sabbath, which is forbidden.

Which may have been ignited on the Sabbath. If, however, the light of the gentile had not been kindled on the Sabbath, it would be allowed.