Look at the greatness of the Prophet (saws), and his mercy and compassion for his nation, for he was sad because they did not believe.

وَاصْبِرْ وَمَا صَبْرُكَ إِلاَّ بِاللّهِ وَلاَ تَحْزَنْ عَلَيْهِمْ وَلاَ تَكُ فِي ضَيْقٍ مِّمَّا يَمْكُرُونَ (128) إِنَّ اللّهَ مَعَ الَّذِينَ اتَّقَواْ وَّالَّذِينَ هُم مُّحْسِنُونَ

{And be patient, [O Muhammad], and your patience is not but through Allah. And do not grieve over them and do not be in distress over what they conspire. Indeed, Allah is with those who fear Him and those who are doers of good} (An-Nahl: 127-128).

The Prophet (saws) used to grieve for those who hasten to disbelief, so Allah (swt) wants to relief the Prophet (saws) so He (swt) moved the matter from the Prophet (saws) and his faithful followers to Him (swt), so says:

إِنَّهُمْ لَن يَضُرُّواْ اللّهَ شَيْئاً {Indeed, they will never harm Allah at all.}: That is, their enmity is with Allah (swt), not with the Prophet of Allah, this is a great supportive power that Allah (swt) gives to His Prophet (saws). Here we will explain more the words of Allah (swt):

﴿وَلاَ يَحْزُنكَ الَّذِينَ يُسَارِعُونَ فِي الْكُفْرِ﴾ {And do not be grieved, [O Muhammad], by those who hasten into disbelief.}: The Prophet (saws), used to grieve when he saw a person whose heart was not open to religion; Because he settled himself in order to get the people out of polytheism and darkness, so his call (saws) was the call of truth, light and goodness, Abdullah bin Amr bin Al-‘Aas, (may Allah be pleased with them) narrated that the Prophet (saws) recited the saying of Allah (swt) about Abraham (PBUH):

رَبِّ إِنَّهُنَّ أَضْلَلْنَ كَثِيرًا مِّنَ النَّاسِ فَمَن تَبِعَنِي فَإِنَّهُ مِنِّي وَمَنْ عَصَانِي فَإِنَّكَ غَفُورٌ رَّحِيمٌ

{My Lord, indeed they have led astray many among the people. So whoever follows me – then he is of me; and whoever disobeys me – indeed, You are [yet] Forgiving and Merciful.} (Ibrahim: 36)

And Issa (PBUH) saying:

إِن تُعَذِّبْهُمْ فَإِنَّهُمْ عِبَادُكَ وَإِن تَغْفِرْ لَهُمْ فَإِنَّكَ أَنتَ الْعَزِيزُ الْحَكِيمُ

{If You should punish them – indeed they are Your servants; but if You forgive them – indeed it is You who is the Exalted in Might, the Wise.} (Al-Maaida: 118)

Then he (saws) raised up his hands and said:

“O Allah! My Ummah, my Ummah,” and wept; Allah, the Exalted, said: “O Jibril (Gabriel)! Go to Muhammad (saws) and ask him: ‘What makes you weep?” So Jibril came to him and asked him (the reason of his weeping) and the Messenger of Allah informed him what he had said (though Allah knew it well). Upon this Allah said: “Jibril, go to Muhammad (saws) and say: ‘Verily, We will please you with regard to your Ummah and will never displease you”.[1]

[1] Sahih Muslim: Chapter of Faith, Hadith No. 202.