The New York Times has perhaps the best report on what we know about the Abedin emails so far. One theory that made a lot of sense to me was that Comey would only have done what he did on Friday if the newly discovered emails were highly significant. But it looks like no one has any idea how significant they are because they haven’t been examined yet:

The F.B.I. offered no comment, and Justice Department officials said they had no idea what Mr. Comey saw as his next move. Justice Department officials were particularly puzzled about why Mr. Comey had alerted Congress — and by extension, the public — before agents even began reading the newly discovered emails to determine whether they contained classified information or added new facts to the case.
Law enforcement officials have begun the process to get court authority to read the emails, officials said. How soon they will get that is unclear, but there is no chance that the review will be completed before Election Day, several law enforcement officials said. Many of the emails are most likely copies of messages that the F.B.I. has already read, said the officials, who spoke on the condition of anonymity because they were not authorized to comment publicly.

And this how the Times describes what the FBI came across:

On Oct. 3, F.B.I. agents seized several electronic devices from Mr. Weiner: a laptop, his iPhone and an iPad that was in large measure used by his 4-year-old son to watch cartoons, a person with knowledge of the matter said. Days later, F.B.I. agents also confiscated a Wi-Fi router that could identify any other devices that had been used, the person said.
While searching the laptop, the agents discovered the existence of tens of thousands of emails, some of them sent between Ms. Abedin and other Clinton aides, according to senior law enforcement officials. It is not clear if Ms. Abedin downloaded the emails to the laptop or if they were automatically backed up there. The emails dated back years, the officials said. Ms. Abedin has testified that she did not routinely delete her emails.
Because of the age of the emails, many could be outside the scope of the Clinton inquiry, investigators said. And while many are probably duplicative, some would be worth reading, the F.B.I. concluded.