From The Art of Lisp & Writing, Richard Gabriel's introduction to David Lamkins' Successful Lisp:
Lisp is the language of loveliness. With it a great programmer can make a beautiful, operating thing, a thing organically created and formed through the interaction of a programmer/artist and a medium of expression that happens to execute on a computer…
The malleability of the medium while programming is part of the act of discovery that goes into understanding all the requirements and forces—internal or not—that a system must be designed around…
Lisp is a medium for working with a computation until it is in balance with its external and internal requirements. At that point it can be decorated with performance-enhancing declarations and perhaps additionally modularized. In this it is more like an artist's medium than what many think of as a programming language.
Lisp, viewed this way, is a good vehicle for understanding how programming and software development really take place. Because programming Lisp is more like writing than like describing algorithms, it fits with how people work better than the alternatives.
Of course, this is the same point that Paul Graham made in Hackers and Painters:
[This] means that a programming language should, above all, be malleable. A programming language is for thinking of programs, not for expressing programs you've already thought of. It should be a pencil, not a pen. Static typing would be a fine idea if people actually did write programs the way they taught me to in college. But that's not how any of the hackers I know write programs. We need a language that lets us scribble and smudge and smear, not a language where you have to sit with a teacup of types balanced on your knee and make polite conversation with a strict old aunt of a compiler.