Imaam As-Sadi (rahimahullaah) said:
Among the benefits of Naseehah (sincere advice) is that it is a safeguard against deceit, for indeed whoever deceives the Muslims in their Religious and Worldly Affairs is not from them. Deceit is among the most repugnant of traits in relation to (fulfilling) the rights of a relative, a non-relative, the person who opposes you and the one in agreement. The Great Qur’aan calls to this quality (i.e. sincere advice), which is from the best of qualities. Indeed, giving sincere advice to every individual is praiseworthy in the divine Islamic Law and it is something in agreement with (sound) intellect and natural disposition. And what is in opposition to it is regarded repulsive in the divine Islamic Law and in opposition to (sound) intellect and natural disposition.
[Source: Abridged & slightly paraphrased. Source: Fat’hul Raheemil Malikil Allaam Fee Ilmil Aqaa-id Wat-Tawheed, Wal Akhlaaq, Wal Ahkaam. Page: 98. Slightly paraphrased]