I highly recommended you to have a look at *An introduction to statistical learning(An introduction to statistical learning book (Tibshirani et. al, 2013).
The reason for this is that Elements of statistical learning book is intended for individuals with advanced training in the mathematical sciences. In the foreword to ISL, the authors write:
An Introduction to Statistical Learning arose from the perceived need for a broader and less technical treatment of these topics. [...]
An Introduction to Statistical Learning is appropriate for advanced undergraduates or master’s students in statistics or related quantitative fields or for individuals in other disciplines who wish to use statistical learning tools to analyze their data.