Thank you, Kaitlin.
I was operating under the belief (as a person of above average intelligence, but no legal background whatsoever) that since I am absolutely intending to sell the t-shirts to as many people as I can convince to buy them, and am interested in the quoted material solely because I think it's so great that it will sell lots of t-shirts... that 'fair use' was right out the window. I'm really not making any kind of political statement, philosophical statement, etc. It's really just "here are some beautiful words - wouldn't you like to wear them?" I just wanted to check and make sure that I was not missing some loophole that would allow me to do things 'the easy way.'
I think for now I will table this particular design idea. I like to sleep the sleep of the just.

If I revisit this concept in the future I will seek the advice of an appropriately experienced attorney. Again, thanks for your input.