Sotah 2a - Zivugin are difficult like krias yam suf

Rashi explains that the statement of the gemara that it is difficult to make zivugin like krias yam suf, is not refering to the bringing together a man and woman, rather it is refering to the ability to make sure that each spouse receives one who is l'fi ma'asav. The gemara then asks from the statement of R' Yehuda in the name of Rav that a spouse is determined for every man (tosafos) already 40 days prior to yetziras havlad. The maharsha points out that this question can simply be on the statement immediatley preceeding which is the statement of "קשה זיווגין כקריעת ים סוף" which implies that Hashem כביכול has a difficult time, yet we find that it is determined before he is even born which implies that it is accomplished without any difficulty. However, Rashi explains the question differently. The question is really on the fact that zivugin are done according to a persons accomplishments (צדיק או רשע), and asks that we find that Hashem sets up shidduchim 40 days prior to yetziras h'vlad before it is determined whether he is a tzadik or rasha. Rashi avoids the maharsha's question, because rashi explains that the statement of קשה זיווגין כקריעת ים סוף is also predicated on אין מזווגין לאדם אלא לפי מעשיו.

This approach of Rashi forces him to deal with the paradox of the Rambam that G-d knows the future, yet one has free choice to choose to be a tzadik or rasha. Rashi answers this paradox by saying הכל בידי שמים חוץ מיראת שמים, which is somewhat ambiguous and implies that although Hashem knows the future about most events, He is unaware about the future of whether a person will be a tzadik or rasha. This is certainly impossible to accept. The maharshal explains that Rashi was never bothered by the paradox between Hashem knowing the future and the freedom of choice, rather rashi was bothered why the gemara assumes that if a zivug is done prior to yetziras h'vlad, it must not be based on merit. Maybe it is based on merit, yet Hashem knows the future. To that Rashi answers that Hashem may know what will be, but will not make a decree with a heavenly voice announcing the zivugin based on that knowledge, because a decree would remove the possibility of choice. Tosafos Harosh explains similarly, but seems to understand that even a decree would not negate free choice, but it would make people doubt the freedom of choice, therefore Hashem would not make a decree based on one's merit prior to them making those decisions.