In The Name of Allaah, The Most Merciful, The Bestower of Mercy
Allaah [The Most High] said:
وَقُل لِّعِبَادِي يَقُولُوا الَّتِي هِيَ أَحْسَنُ ۚ إِنَّ الشَّ بَيْنَهُمْ ۚ إِنَّ الشَّيْطَانَ كَانَ لِلْإِنسَانِ عَدُوًّا مُّبِينًا
And say to My slaves that they should (only) say those words that are the best. (Because) Shaitan (Satan) verily, sows disagreements among them. Surely, Shaitan (Satan) is to man a plain enemy.
Allaah [The Blessed and Most High] command His slave and Messenger [i.e. Muhammad (sallal-laahu-alayhi-wasallam)] to command Allaah’s believing slaves that they speak to one another in their conversations and discussions with what is better and good, for if they do not do that, shaytaan will initiate a state of conflict between them and speech will lead to actions, and thus evil, [blameworthy] argumentation and fighting will arise; for indeed shaytaan is an enemy of Aadam and his children since [the time] he refused to prostrate to Aadam. His enmity is clear and manifest, so because of this it prohibited for a man to point at his Muslim brother with an iron [instrument], for indeed shaytaan [can entice an evil action] in his hand and he may strike [ his Muslim brother] with it. [Ref 1]
Imaam Sadi stated that this command [i.e. in Surah Al-Israa Aayah 53] is related to every speech that will bring a person close to Allaah, such as recitation [of the Qur’aan], remembrance of Allaah, enjoining good and forbidding evil, [to address the people] with good and gentle speech in accordance with their different social statuses and positions. If something resolves around two good affairs, then Allaah commands that the better of the two is chosen if it is not possible to combine both of them. Good speech leads to every beautiful mannerism and righteous deed, for indeed the one who controls his tongue will be able to take control of his affairs.
Shaytaan wants to cause disagreements between you. He hastens towards that which will corrupt the religious and worldly affairs of the slaves. Therefore, the remedy for this is that he is not to be followed when he incites you to utter statements that are not good in order to cause enmity and disagreements between you. He is your real enemy and it is obligated on you to wage war against him because he calls you to be among the people of the hell fire. [Ref 2]
[Ref 1: Source: Al-Misbaah Al-Muneer Fee Tahdheb Tafseer Ibn katheer’ Surah Al-Israa 17: 53]
[Ref 2: Paraphrased & Abridged…see Tayseer Al-kareem ar-Rahmaan Fee Tafseer Kalaam al-Mannaan]