الدِّينُ النَّصِيحَةُ.
Religion is sincere counsel and genuine goodwill.
Source: Muslim (as cited in the book).
ArabicMeaning
الدِّينُreligion; a life of obedience to Allah
النَّصِيحَةُsincerity, goodwill, trustworthy advice
نَصِيحَة is not mere criticism or fault-finding. It is sincerely seeking what is right and beneficial, expressed with honesty, trustworthiness, and an appropriate manner. The phrase is a nominal sentence: الدِّينُ is the subject and النَّصِيحَةُ the predicate.
The forceful wording shows that sincere counsel has exceptional importance in religion, not that the other obligations of religion disappear.