There is another version of the text of the fourth oath, cited by Rashi, that reads “shelo yerachaku” – that they should not push the end of exile further away. Rashi explains, “They should not push the end further away with their sin.”
This is also difficult to understand: which sin is Rashi talking about? If he means any sin in the Torah, why did Hashem need to impose an oath on the Jewish people not to sin? We are already foresworn since Mount Sinai not to transgress any part of the holy Torah, and one oath cannot take effect when there is a pre-existing oath, as the Gemara says (Nedarim 8a and other places). And if Rashi means that there is one particular sin that delays the redemption, then he should have specified which one it is.
The Midrashim seem to have had the version that reads “shelo yidchaku” (they should not force the end) because they cite as an example the Bnei Ephraim’s early escape from Egypt, Ben Koziva’s uprising, and other examples of forcing one’s way out of exile before the time. The commentators also seem to understand the oath as “forcing the end” and not “pushing the end further away.”
[In Siman 84 the Rebbe will answer that the particular sin Rashi had in mind was the violation of the Oaths: attempting to end the exile early actually backfires and causes the exile to be extended.]