Gains of Being Sincere

Imaam Ibn Qayyim al-Jawziyyah stated: 

The unchangeable observed law of Allah and His unalterable way is to enshroud a sincere person with dignity, light and love in the hearts of the creatures and drawing their hearts closer to him in proportion to his sincerity, intention and dealings with his Lord. And He will cover an insincere person who puts on the garment of falsehood with detestation, humiliation and revulsion that befit him. Therefore, a sincere person will have dignity and love while the other will gain abhorrence and hatred.

Source: ’laam al-Muwaqqi‘een ‘an Rabb al-‘Aalameen by Ibn Qayyim al-Jawziyyah

The Basic Cause of Misguidance

Shaykh al-Islam Ibn Taymiyyah (may Allah have mercy on him) stated:

The foundation of misguidance among the inhabitants of the earth stems from two things: either regarding as part of religion that which was not legislated by Allah, or regarding as Haraam that which was not forbidden by Allah. Consequently, the basic principle on which Imam Ahmad and other Imams based their schools of fiqh is that:  people’s deeds are divided into two categories: acts of worship that they take as part of their religion, by means of which they may benefit in the Hereafter, or in this world; and customs which are of benefit to them in their daily lives. So, the basic principle concerning acts of worship is that nothing is to be prescribed except that which was legislated by Allah while the basic principle concerning customs is that nothing is to be forbidden except that which was forbidden by Allah.

Source: Sharh Iqtidaa as-Siraat al-Mustaqeem, p. 322 of Shaykh al-‘Uthaymeen