Allah addresses His Messenger and reminds him and the believers of the favor that He has made his heart and words soft for his Ummah, those who follow his command and refrain from what he prohibits.

﴿فَبِمَا رَحْمَةٍ مِّنَ اللَّهِ لِنتَ لَهُمْ﴾

(And by the mercy of Allah, you dealt with them gently) ﴿3:159﴾. meaning, who would have made you this kind, if it was not Allah's mercy for you and them. Qatadah said that,

﴿فَبِمَا رَحْمَةٍ مِّنَ اللَّهِ لِنتَ لَهُمْ﴾

(And by the mercy of Allah, you dealt with them gently) means, "With Allah's mercy you became this kind.'' Al-Hasan Al-Basri said that this, indeed, is the description of the behavior that Allah sent Muhammad with. This Ayah is similar to Allah's statement,

﴿لَقَدْ جَآءَكُمْ رَسُولٌ مِّنْ أَنفُسِكُمْ عَزِيزٌ عَلَيْهِ مَا عَنِتُّمْ حَرِيصٌ عَلَيْكُمْ بِالْمُؤْمِنِينَ رَءُوفٌ رَّحِيمٌ ﴾

(Verily, there has come unto you a Messenger from among yourselves. It grieves him that you should receive any injury or difficulty. He is anxious over you (to be rightly guided, to repent to Allah); for the believers (he is) full of pity, kind, and merciful) ﴿9:128﴾. Allah said next,

﴿وَلَوْ كُنْتَ فَظّاً غَلِيظَ الْقَلْبِ لاَنْفَضُّواْ مِنْ حَوْلِكَ﴾

(And had you been severe and harsh-hearted, they would have broken away from about you;)

The severe person is he who utters harsh words, and,

﴿غَلِيظَ الْقَلْبِ﴾

(harsh-hearted) is the person whose heart is hard. Had this been the Prophet's behavior, "They would have scattered from around you. However, Allah gathered them and made you kind and soft with them, so that their hearts congregate around you.'' `Abdullah bin `Amr said that he read the description of the Messenger of Allah in previous Books, "He is not severe, harsh, obscene in the marketplace or dealing evil for evil. Rather, he forgives and pardons.''