The gemara in Gittin [24a] says:
האשה עצמה מביאה וכו': אשה מכי מטי גיטה לידה איגרשה לה אמר רב הונא באומר לא תתגרשי בו אלא בפני ב"ד פלוני סוף סוף כי מטיא התם איגרשה בה
The mishna teaches that the woman herself may bring her own bill of divorce and state that it was written and signed in her presence. The Gemara asks: Why does she need to bring it and testify that it was written and signed in her presence? With regard to this woman, once her bill of divorce reaches her hand, she is divorced.
Rashi writes that she shouldn't have to say בפני נכתב because she is not a שליח and was already divorced with the get she is holding. The Rambam also writes in Hilchos Geirushin [12-2] that a woman who appears with a get is believed that the get is a valid one and may get married without a קיום הגט [validation].
The Raavad and the Rashba argue and say that a woman who brings her get requires קיום. They apparently understand the question of the gemara אשה מכי מטי גיטה לידה איגרשה לה - to be saying that since she is the one getting divorced, she has the status of a בעל דבר and not a שליח and is thus not believed. Therefore, an external validation is required.
The Rambam invests effort in explaining his shittah and writes [7-24]
לא נחוש וכו' לאשה עצמה שהגט יוצא מתחת ידה שאין דיני האיסורין כדיני הממונות
We can believe the woman who is holding the get because the laws of איסורין are not like the laws of ממונות.
Apparently what he means is that when it comes to ממונות we claim that the שטר is מזוייף [a forgery] on behalf of the בעל דבר because there is a בעל דבר whom we want to attempt to protect. But when it comes to איסורין, there is no בעל דבר so there is no reason to claim that the get is מזוייף. This reveals that the Rambam understands the reason for not claiming מזוייף differently than Tosfos [2a ד"ה ואם] who say that it is because in cases of עגונה the rabbis were lenient.
Apparently, the Rashba and Raavad argue on this point and maintain that דיני איסורין are like דיני ממונות and we require קיום on the get even if the husband doesn't challenge it just as we do with שטרי ממון. But this can't be because it would contradict an explicit mishna that says that if one brings a get in Eretz Yisrael, he need not say בפני נכתב and it doesn't require קיום unless the husband challenges its validity.
Therefore we must say that the Rashba and Raavad don't equate a get with שטרי ממון rather חכמים decreed that all gittin coming from overseas require a קיום. They also decreed that בפני נכתב validates the get in lieu of a קיום. So there were 2 takanos - 1] We require קיום. Two - בפני נכתב also works. Therefore, the woman who brings the get and lacks the נאמנות of a שליח requires קיום. This is all regarding a get that came from chutz la-aretz. But when the get came from Eretz Yisrael, no קיום was ever required.
Rashi and the Rambam argue and hold that קיום was never required for a get, only בפני נכתב. Since she need not say בפני נכתב, the get is valid. According to them, saying בפני נכתב is not a קולא instead of actual קיום [as according to the other Rishonim] but a חומרא.
[עפ"י שיעורי הרב]
LOTTTTTSSS to talk about. May Hashem give me the life and health and financial means to do so....:-)