That’s frog for “To set an example for the others“, and that’s precisely why this WH will never, ever, give Snowden any form of clemency. In fact, if they ever do, Snowden is advised to decline, albeit politely, under the expectation that they are lying to him so they can get him, and then, they will punish him. Nobody lies as often and with such aplomb as the members of this “The most ethical administration, EVAH!” do.
Even the left, and Slate is left leaning, if anything, admits that this administration punishes those that blow the whistle at their abuses. And they knew this was the case long before the Snowden incident as the date of that Slate article clearly shows. Get in their way and they will use every means and agency of the government to bury you. Snowden will have to wait until someone else is in charge to have a chance at a pardon for doing the American people a service.