[21:107] وَمَا أَرْسَلْنَاكَ إِلَّا رَحْمَةً لِّلْعَالَمِينَ

And [thus, O Prophet,] We have sent thee as [an evidence of Our] grace towards all the worlds. [Asad]

The Prophet (PBUH) was sent to all the worlds with proof and evidence in support of the truth of his message and was told to present it in a beautiful and endearing way:

ادْعُ إِلَىٰ سَبِيلِ رَبِّكَ بِالْحِكْمَةِ وَالْمَوْعِظَةِ الْحَسَنَةِ ۖ وَجَادِلْهُم بِالَّتِي هِيَ أَحْسَنُ ۚ إِنَّ رَبَّكَ هُوَ أَعْلَمُ بِمَن ضَلَّ عَن سَبِيلِهِ ۖ وَهُوَ أَعْلَمُ      [16:125] بِالْمُهْتَدِينَ

O Messenger! Do not entangle yourself with them. You continue your program of inviting people to the way of Allah with wisdom and kindly exhortation and discuss matters with them in the best possible manner. Allah knows best who is following the right path and who has gone astray.

Speak in a way that touches the heart:

[4:63]  وَقُل لَّهُمْ فِي أَنفُسِهِمْ قَوْلًا بَلِيغًا

And speak with them about themselves which enters straight into their heart.

This will help those – who still have in their hearts even a small desire to accept the truth – to avoid falling into hell, the pit of destruction.

 [6:70]  وَذَكِّرْ بِهِ أَن تُبْسَلَ نَفْسٌ بِمَا كَسَبَتْ

Leave them alone but continue to convey to them the teachings of the Quran so that none is destroyed through not receiving Allah’s guidance.

As for others who are utterly arrogant and argumentative and in total denial of this message, there is no hope for them because their hearts are dead:

 إِنَّكَ لَا تُسْمِعُ الْمَوْتَىٰ وَلَا تُسْمِعُ الصُّمَّ الدُّعَاءَ إِذَا وَلَّوْا مُدْبِرِينَ ; وَمَا أَنتَ بِهَادِي الْعُمْيِ عَن ضَلَالَتِهِمْ ۖ إِن تُسْمِعُ إِلَّا مَن يُؤْمِنُ  بِآيَاتِنَا فَهُم مُّسْلِمُونَ
[27:80-81]

You can only talk to those whose hearts are alive and open. You can neither make those whose hearts are dead listen to you, nor can you make the deaf hear your call; particularly if their attitude is such that they turn their faces away when you call them. Neither can you show the straight path to the blind, i.e., those who do not even want to open their mind’s eye! Therefore, do not waste your time over them (36:10). Because of their intransigence Allah’s law has put chains around their necks, and built barriers behind and in front of them [36:7-9].

The only people who will listen to you are those who are willing to open their hearts for the divine truth; are willing to pay attention to what is being said to them; and are prepared to ponder and think. They will thus believe in the truthfulness of Our Laws and thereafter submit before them wholeheartedly.

And do not get disheartened because they do not listen to you although what you say is based on truth, knowledge and wisdom. Only those who use their minds and use logic will be able to comprehend this divine message. How can anyone who is blinded by his emotions and is devoid of his faculty of thinking, do so? Therefore do not be disheartened that they do not listen to you.

 [36:70]  لِّيُنذِرَ مَن كَانَ حَيًّا وَيَحِقَّ الْقَوْلُ عَلَى الْكَافِرِينَ

And O Messenger! This code of life has been given to you so that you may warn the people who still exhibits signs of spiritual life and want to survive. If they still refuse to adopt the right path, they will themselves see that whatever We had said was the truth.

In fact, warning those who are traveling on wrong path in their journey of life, that they are headed for destruction, is also a form of glad tiding. Warning people to take appropriate shelter because a severe tornado is approaching is actually good news for them for their own safety and well being. Ignoring this warning is actually inviting their own death and destruction. This is the purpose of the warning by the Quran:

 [18:2-3]  قَيِّمًا لِّيُنذِرَ بَأْسًا شَدِيدًا مِّن لَّدُنْهُ وَيُبَشِّرَ الْمُؤْمِنِينَ الَّذِينَ يَعْمَلُونَ الصَّالِحَاتِ أَنَّ لَهُمْ أَجْرًا حَسَنًا ; مَّاكِثِينَ فِيهِ أَبَدًا

It gives warning of a grievous chastisement to the non-believers and announces to the believers who do right things with glad tidings – that blessings from Allah await them; a home wherein they shall abide beyond the count of time. And:

وَكَذَٰلِكَ أَوْحَيْنَا إِلَيْكَ قُرْآنًا عَرَبِيًّا لِّتُنذِرَ أُمَّ الْقُرَىٰ وَمَنْ حَوْلَهَا وَتُنذِرَ يَوْمَ الْجَمْعِ لَا رَيْبَ فِيهِ ۚ فَرِيقٌ فِي الْجَنَّةِ وَفَرِيقٌ فِي السَّعِيرِ
[42:7]
This clear and explicit Code of Laws has been revealed to you so that firstly you can caution people living in and around Makkah about the destructive results of their erroneous way of life. Then warn them that, if they do not abandon this way of life then, for the final decision on this tussle, all groups will be gathered in an open field. One group will enter heavenly society (as victors) while the others will fall in the ditch of Hell (as losers). Tell them that this is undoubtedly bound to happen. And history bears testimony that this did happen.

The messenger himself has been called a warner:

يَا أَيُّهَا النَّبِيُّ إِنَّا أَرْسَلْنَاكَ شَاهِدًا وَمُبَشِّرًا وَنَذِيرًا

O Prophet! As far as you are concerned We have sent you to establish a Divine System which will also supervise the performance of all nations (2:43). You will be the bearer of glad tidings to the people who follow this System; and warn them about the destructive results of disobeying it [33:45, 28:46, 38:65, 46:9, 48:8, 51:51, and 53:56].

As mentioned, the other facet of the warning is glad tiding. But when someone is told that his wrong path of life will lead to destruction and hell – then this is the negative aspect of the warning. Its positive aspect is that the correct path will lead him to success and to heavenly life. This is the glad tiding for those who do righteous deeds. So, warning and glad tiding are, in fact, two lines of the same couplet, two branches of the same root, two sides of the same coin:

 [46:12]  وَمِن قَبْلِهِ كِتَابُ مُوسَىٰ إِمَامًا وَرَحْمَةً ۚ وَهَـٰذَا كِتَابٌ مُّصَدِّقٌ لِّسَانًا عَرَبِيًّا لِّيُنذِرَ الَّذِينَ ظَلَمُوا وَبُشْرَىٰ لِلْمُحْسِنِينَ

As has been mentioned before, the book revealed earlier to Moses was a code of correct guidance and a source of mercy for human beings. However, it did not stay in its original form. Now this Book has been sent to practically prove the claims mentioned in that earlier book. This Book (the Quran) has been revealed in an explicit clear language (Arabic), so that you can warn those who have left the right course and have adopted aggressive and unjust ways. Also you can give glad tidings to those who lead balanced and righteous lives.

Therefore, Prophet Muhammad (PBUH) was both a warner and a source of glad tidings to all humankind:

[2:119] إِنَّا أَرْسَلْنَاكَ بِالْحَقِّ بَشِيرًا وَنَذِيرًا ۖ وَلَا تُسْأَلُ عَنْ أَصْحَابِ الْجَحِيمِ

It is in accordance with Our Plan that We have sent you, O Messenger, with truth so that you may give glad tidings to those who live in accordance with Allah’s Revelation; and a warning to those who do the opposite. If the latter do not pay heed to your warning then they would be destroyed and become companions of hell – and you will not be held responsible for their agonizing end.