In almost every language but Modern English, people knew whether the speaker was addressing one person or many. In Classical English, this is preserved. If the speaker is talking to one person, he uses "thee" or "thou." If he is talking to many people, he says "you" or "your." The King James preserves this distinction.
When Jesus spoke to Nicodemus, He said, "Marvel not that I said unto thee, ye must be born again" (John 3:7). What He said in effect was, "Marvel not that I said unto thee (Nicodemus), ye (all of you people) must be born again." Jesus did not tell this only to Nicodemus.
He spoke to all people of all times, from those who stood around that night, even to us today: Ye must be born again!
From The King James Bible Companion by David W. Daniels.