Comma Rule #8. Commas to set off quotes:
If you are leading into a quote with a verb, put a comma after the verb and then insert your quote.
It is important to remember that you can also use a colon to set off a quote.
If a quote is four or more lines long, separate the quote as a paragraph introduced with a colon, whether the preceding word is a verb or not.
In his book Walden, Thoreau wrote:
A single footstep will not make a path on the earth, so a single thought will not make a pathway in the mind. To make a deep physical path, we walk again and again. To make a deep mental path, we must think over and over the kind of thoughts we wish to dominate our lives.
[Note: I like the quotes in italics, but this is not a rule." You don't need the quotation marks because the indentation and context indicates the quote. Be sure to block quote the entire quote--don't center it!!!]