Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) once mentioned the following:
The essence of Deen is for a person to make his heart and desires (likes and dislikes) conform to the command of Allah Ta‘ala at all times. (When one’s heart and desires conform to the command of Allah Ta‘ala, then practicing upon every law will be easy for him). Deen is not confined to merely acquiring the knowledge of the various masaa-il and rulings of Islam. (Acquiring the knowledge of the various masaa-il and rulings of Islam is extremely important, but practicing upon them is equally important as this is what makes one a true believer. However, together with acquiring the knowledge of Deen and practicing upon the laws, one should make an effort to make his heart and desires conform to the command of Allah Ta‘ala at all times). When one looks at the ‘Ulama of the Jews, then one finds that they possessed immense knowledge of their sharee‘ah, but the thing lacking in them was that they did not practice on their Deen. The reason for them not practicing upon their Deen was that their hearts and desires did not conform to the command of Allah Ta‘ala. It is for this reason that they became deserving of the divine wrath of Allah Ta‘ala and were rejected from His mercy.
(Malfoozaat Hazrat Moulana Muhammad Ilyaas (rahmatullahi ‘alaih) pg. 99)
Source: Ihyaauddeen.co.za