Cryptanalysis is absolutely essential to cryptography, albeit in a somewhat negative sense. That is, the only thing that tells you that your cryptographic steps are worthwhile is the fact that cryptanalysis has failed, despite the longstanding efforts of smart and knowledgeable cryptanalysts. Think of this in the same way as automobile crash tests. To test the safety of a car, it's essential to run a few of them into some brick walls to see just where the failure points arise.

You will not be a cryptanalyst after finishing this tutorial. To do that, you need many years of mathematical study, a good mind for a certain way of thinking, and a considerable number of failed attempts at cryptanalysis. Nonetheless, having a general concept of what cryptanalysis does is an essential part of understanding what it means to create cryptographic programs. You might not be able to demonstrate that your protocols are secure, but at least you will know what it means to demonstrate that they are not.