What does the rebus mean? The rebus is as follows: It is very necessary.
It is obviously
Brainy Smurf (Schtroumpf à Lunettes in the original french version).
This is a king missing an I (or an eye). And as we know it : in the land of the blind, the one-eyed man is king.
So, this is a kingdom full of blind people. Also, the king is blue. The only logical explanation is that this is the Smurf village where all Smurfs went blind (because of some Gargamel's trick or whatever). And which Smurf managed to keep at least an eye in working condition ? The one wearing eye-protection of course. Glasses.
Hence : Brainy Smurf.
A possible answer is:
A just king.
A just king with perspective.
The king has no "i" (or "no eye") and as justice is blind, so is the king —a just king. And there is the possible addition of the word "perspective" as the letters are shown at a perspective angle. And I would say "It is very necessary" for a king to be just and have perspective.
Another possible variant:
A king with a just perspective.