I'm find that this is a good resource to help explain the "why's" behind this great catechism.
I recommend it for sure.
The Heidelberg Catechism is one of the finest creeds of the reformation period. A faithful teacher of millions, it has stood the test of time and is still, today, one of the best tools available for learning what it means to be a Christian. This study guide to the Catechism includes 129 questions and answers, along with clear exposition and questions for review, further study, and discussion.
G.I. Williamson is a semi-retired minister in the Orthodox Presbyterian Church and editor of Ordained Servant. He has written several books, including The Westminster Confession of Faith: For Study Classes and The Heidelberg Catechism: A Study Guide.