And We have sent you not but as a mercy for the `Alamin.
Here Allah tells us that He has made Muhammad a mercy to the `Alamin, i.e., He sent him as a mercy for all of them (peoples), so whoever accepts this mercy and gives thanks for this blessing, will be happy in this world and in the Hereafter. But whoever rejects it and denies it, will lose out in this world and in the Hereafter, as Allah says;
أَلَمْ تَرَ إِلَى الَّذِينَ بَدَّلُواْ نِعْمَتَ اللَّهِ كُفْرًا وَأَحَلُّواْ قَوْمَهُمْ دَارَ الْبَوَارِ
جَهَنَّمَ يَصْلَوْنَهَا وَبِيْسَ الْقَرَارُ
Have you not seen those who have changed the blessings of Allah into disbelief, and caused their people to dwell in the house of destruction Hell, in which they will burn, -- and what an evil place to settle in! (14;28-29)
And Allah says, describing the Qur'an;
قُلْ هُوَ لِلَّذِينَ ءَامَنُواْ هُدًى وَشِفَأءٌ وَالَّذِينَ لَا يُوْمِنُونَ فِى ءَاذَانِهِمْ وَقْرٌ وَهُوَ عَلَيْهِمْ عَمًى أُوْلَـيِكَ يُنَادَوْنَ مِن مَّكَانٍ بَعِيدٍ
Say;"It is for those who believe, a guide and a healing. And as for those who disbelieve, there is heaviness in their ears, and it is blindness for them. They are those who are called from a place far away." (41;44)
Muslim reports in his Sahih;Ibn Abi `Umar told us, Marwan Al-Fazari told us, from Yazid bin Kisan, from Ibn Abi Hazim that Abu Hurayrah said that;
it was said, "O Messenger of Allah, pray against the idolators."
He said;
إِنِّي لَمْ أُبْعَثْ لَعَّانًا وَإِنَّمَا بُعِثْتُ رَحْمَة
I was not sent as a curse, rather I was sent as a mercy.
This was recorded by Muslim.
Imam Ahmad recorded that `Amr bin Abi Qurrah Al-Kindi said;
"Hudhayfah was in Al-Mada'in and he was mentioning things that the Messenger of Allah had said.
Hudhayfah came to Salman and Salman said;`O Hudhayfah, the Messenger of Allah (would sometimes be angry and would speak accordingly, and would sometimes be pleased and would speak accordingly. I know that the Messenger of Allah) addressed us and said;
أَيُّمَا رَجُلٍ مِنْ أُمَّتِي سَبَبْتُهُ سَبَّةً فِي غَضَبِي أَوْ لَعَنْتُهُ لَعْنَةً فَإِنَّمَا أَنَا رَجُلٌ مِنْ وَلَدِ ادَمَ أَغْضَبُ كَمَا تَغْضَبُونَ إِنَّمَا بَعَثَنِي اللهُ رَحْمَةً لِلْعَالَمِينَ فَاجْعَلْهَا صَلَةً عَلَيْهِ يَوْمَ الْقِيَامَة
Any man of my Ummah whom I have insulted or cursed when I was angry -- for I am a man from among the sons of Adam, and I get angry just as you do. But Allah has sent me as a Mercy to the Worlds, so I will make that (my anger) into blessings for him on the Day of Resurrection."
This was also recorded by Abu Dawud from Ahmad bin Yunus from Za'idah.
It may be asked;what kind of mercy do those who disbelieve in him get?
The answer is what Abu Jafar bin Jarir recorded from Ibn Abbas concerning the Ayah;
وَمَا أَرْسَلْنَاكَ إِلاَّ رَحْمَةً لِّلْعَالَمِينَ
(And We have sent you not but as a mercy for the `Alamin), He said,
"Whoever believes in Allah and the Last Day, mercy will be decreed for him in this world and in the Hereafter;
whoever does not believe in Allah and His Messenger, will be protected from that which happened to the nations of earthquakes and stoning."