When you first start studying functional programming, one of the things that people will ask you is “So; have you learned lambda calculus (TLC)?”.
The fact is that while you don’t need to learn TLC to learn about functional programming; you ought too study the TLC at some point.
In this great LtU thread on “where to get started with studying programming language theory”, Anton van Straaten posted a comment referencing two posts on the PLT discussion list detailing a plan on what you should study when it comes to TLC and the texts that you should use to facilitate those studies.