What is the Purpose of Kindergarten?

I recently came across a question on www.answers.com that asked "What is the purpose of Kindergarten?" I was intrigued by the question, but then I read the answer. It stated "busy people who can't take care of their kids and have jobs use kindergarten. its like a daycare thing." This convinced me even more to begin a blog about how to prepare your child for Kindergarten. If you would like to see the post for yourself click the link below.
http://www.answers.com/Q/What_...

Yes, Kindergarten is probably the first time the parents are able to go to work without paying for full-time child care. I can agree with that, because it is a factual statement.

No, it is not for parents who can't take care of their kids. It is for kids who are ready to learn and develop their minds.

So after thinking about this question, I had a question. Is Kindergarten mandatory in the United States? I know in Arizona it is not mandatory. After doing some research I found a website called the Education Commission of the States. There were some interesting facts. In summary, as of September 2016 only 13 states plus the District of Columbia required full day Kindergarten. See the link below to read more about full day Kindergarten.
https://www.ecs.org/?s=kinderg...

What is the purpose of Kindergarten?
The purpose of Kindergarten is to provide a child a solid foundation for their career of education. A foundation of letters and sounds, number sense, shapes and measurement, addition and subtraction, reading and writing. This is just a short list of what a child learns in Kinder. Think of it this way Kindergarten is a pre-requisite for 1st grade. A person cannot join the next class without gaining the knowledge given by the previous class. This is same concept for Kindergarten. It can provide a child a foundation of knowledge to take with them as they enter 1st grade.