While in reading this book Kreeft does spend some time talking about God and his Christian faith, his arguments are philosophically and scientifically sound across the religious spectrum. Regardless of a reader's religion/athiesm, Kreeft's logic applies. While Kreeft argues that morality comes from God, he also demonstrates that one need not know that or believe in God to understand and use objective morals.
This book is highly recommended for all readers who need help with a good strategy for making choices. It would also make an excellent gift for the person in your life who constantly argues that their morality is relative.