"One of the most important advantages of functional programming is that it allows interactive testing. In purely functional code, you can test each function as you write it. If it returns the values you expect, you can be confident that it is correct."
"In Common Lisp, values have types, not variables.You could imagine that every object had a label attached to it, identifying its type."
"What is Lambda? The lambda in a lambda expression is not an operator. It is just a symbol. In earlier dialects of Lisp it had a purpose: functions were represented internally as lists, and the only way to tell a function from an ordinary list was to check if the first element was the symbol lambda."
The option to trade between write a program fast and write a fast program is indeed powerful and differentiate Lisp from other programming languages, and it is indeed important to know that the programming language you use would restrict the way you think, and it is definitely the truth.