The Gemara says that one who begins with HaMaariv Aravim in the morning and ends with Yotzer HaMeoros is Yotzei, not because of how he ended but because it says Golel Or in that Bracha. Conversely, because it says Uvorei Choshech in the morning blessing.
However, if so, why is he not Yotzei in the case of ending with HaMaariv Aravim in the morning, since he said Yotzer Or when he started the Bracha?
Mr. Mordechai Perlman, Jerusalem, Israel
The Chidushei ha'Rashba writes that it is obvious that whenever the end of the Berachah (the "Chasimah") is incorrect, it is considered that nothing at all has been said. The Rashba writes that everyone agrees that the most important thing is the end of the Berachah. The question of the Gemara is whether the Chasimah is so important that even if the beginning ("Pesichah") of the Berachah is wrong, the Chasimah can still amend for it, but everyone will agree that if the Chasimah is bad this ruins the entire Berachah.
The Rashba writes that when the person began the blessing in the morning with "ha'Ma'ariv Aravim," this was considered a good Pesichah since he also needed to say "Golel Or," a reference to the morning, in the Berachah. Therefore, when he concludes with "Yotzer Or" it follows that he has both a good Pesichah and a good Chasimah. In contrast, if he concludes with "ha'Ma'ariv Aravim," he is not Yotzei because it is essential that he has the correct conclusion of "Yotzer ha'Me'oros."
This Halachah is also mentioned by the Mishnah Berurah (OC 59:4) that everyone agrees that the Chasimah must certainly be correct.
Kol Tuv,
Dovid Bloom