In Wind Waker, the Master Sword’s true power is sealed when Link first obtains it. The guard starts out closed, but opens up as Link visits the temples to unlock its power.
Also, in the context of the parent post, this is poking fun at the fact that Toon Link has no problem wielding the master sword as a kid, while OOT Link had to suffer through that whole seven year timeskip business in order to do the same thing.
