The Bible says, "Thou shall not kill”. Does this mean the same as: You shall not kill? The problem is that English has four words for you, but only one is in common use today. These other forms of you are only used in certain situations, such as when talking about religion, Shakespeare or poetry, but not much else.
The word you used to be only used for the plural. After the (Norman) French invaded and ruled England the word you also got used as a polite singular. In French, the word for you is vous or tu. It is polite to use the plural vous, instead of the singular tu. When French speakers ruled England being impolite to them could cause your head to be cut off.
Today the word you is used both for the subject and object of a sentence. For example, the word I is used for the subject of the sentence and me is used for the (direct or indirect) object of the sentence. Both I and me are from Old English. Using different words (with a different case) for the subject and the object of a sentence is a feature of many European languages including Modern German and Old English.
I gave it to Tom. (I is the subject of the sentence, Tom is the object.)
Tom gave it to me. (Tom is the subject of the sentence, me is the object.)
The old singular forms of you are thou and thee. They survive in a few traditional uses. Many, but not all, translations of the Bible keep thou instead of you when giving instructions that must be obeyed personally and not as a general instruction to a group. For example: Exodus 20 as well as most of Leviticus and Deuteronomy. Historically thou and thee sounded friendly and casual. They were not as formal as the word you.
The four words for you, with quotations from the Bible* and a regular example:
thou - singular, subject
Thou shall not kill.
Thou gave it to Mary.
thee - singular, object
The Lord your God has commanded thee.
Mary gave it to thee.
ye - plural, subject
Ye shall not eat the blood.
Ye have a maths test next week.
you - plural, object
Whatever has no fins nor scales in the waters, that shall be an abomination to you.
Maths tests are good for you.
Today the word you is singular, plural, subject and object. Always make it clear if you are including only one person being spoken to or the group. The sentence, You have failed your maths test., might be replied to with: Do you mean just me or the whole class? In the Bible, “Thou shall not kill” means you the one-person (male) reading this must not kill people. It does not mean society as a whole; Biblical society had a death sentence. Because of the loss of these other words we must be extra careful using the word you in Modern English.
* The quotations were slightly edited for simplicity. Words such as shalt were changed to shall &c. The quotations are from: Exodus 20:13, Deuteronomy 26:16, Deuteronomy 12:16 and Leviticus 11:12.