Previously the government needed at least a warrant and probable cause to access private records. The Fourth Amendment, Title III of the Omnibus Crime Control and Safe Streets Act of 1968, and case law provided that if the state wished to search you, it needed to show probable cause that a crime had been committed and to obtain a warrant from a neutral judge. Under FISA—the 1978 act authorizing warrantless surveillance so long as the primary purpose was to obtain foreign intelligence information—that was somewhat eroded, but there remained judicial oversight. And under FISA, records could be sought only "for purposes of conducting foreign intelligence" and the target "linked to foreign espionage" and an "agent of a foreign power." Now the FBI needs only to certify to a FISA judge—(no need for evidence or probable cause) that the search protects against terrorism. The judge has no authority to reject this application. DOJ calls this "seeking a court order," but it's much closer to a rubber stamp. Also, now the target of a search needn't be a terror suspect herself, so long as the government's purpose is "an authorized investigation ... to protect against international terrorism."
Downplaying the extent of these changes, the DOJ argued to Congress that 215 is no big deal, since grand juries could always subpoena private records in the past. The difference they don't acknowledge is that investigators may now do so secretly, and these orders cannot be contested in court.