Legal phraseology abounds in double- or triple-barreled expressions:
cease and desist
assault and battery
free and clear
null and void
transfer, convey and assign
will and testament
breaking and entering
This kind of repetition is known as tautology.
As a rhetorical device, tautology can be used to create a desired effect. For example, when Shakespeare put this line in Antony’s mouth in Julius Caesar, he was aiming to create a sense in the listener that the wound made by Brutus was not just a stab wound, but a really, really rotten way to treat a friend:
This was the most unkindest cut of all.
On the other hand, a 21st century student who wrote “That’s the most rudest person I know,” would simply be revealing ignorance of the English system of comparison. This kind of tautology is called pleonasm.
Other examples of pleonasm:
Tautology in the phrasing of legal documents could be seen as a crafty ploy on the part of lawyers to close as many loopholes as possible, but there is a linguistic reason for the existence of these repetitious constructions.
Much of our legal phraseology derives from a time when speakers of Norman French ruled a populace that included many English speakers. At this time also, Latin was still in wide use for certain types of documents. In such a setting, vocabulary was in flux. The laws were often phrased redundantly using words of varying linguistic origin.