فَقُل رَّبُّكُمْ ذُو رَحْمَةٍ وَسِعَةٍ

(Say: "Your Lord is the Owner of vast mercy...") encouraging them to seek Allah's vast mercy and follow His Messenger,

وَلاَ يُرَدُّ بَأْسُهُ عَنِ الْقَوْمِ الْمُجْرِمِينَ

(and never will His wrath be turned back from the people who are criminals.) discouraging them from defying the Messenger, the Final Prophet, Muhammad ﷺ. Allah often joins encouragement with threats in the Qur'an. Allah said at the end of this Surah:

إِنَّ رَبَّكَ سَرِيعُ الْعِقَابِ وَإِنَّهُ لَغَفُورٌ رَّحِيمٌ

(Surely, your Lord is swift in retribution, and certainly He is Oft-Forgiving, Most Merciful.) 6:165 Allah also said,

وَإِنَّ رَبَّكَ لَذُو مَغْفِرَةٍ لِّلنَّاسِ عَلَى ظُلْمِهِمْ وَإِنَّ رَبَّكَ لَشَدِيدُ الْعِقَابِ

(But verily, your Lord is full of forgiveness for mankind in spite of their wrongdoing. And verily, your Lord is (also) severe in punishment.) 13:6, and

نَبِّىءْ عِبَادِى أَنِّى أَنَا الْغَفُورُ الرَّحِيمُ - وَأَنَّ عَذَابِى هُوَ ٱلْعَذَابُ ٱلْأَلِيمُ

(Declare unto My servants, that truly, I am the Oft-Forgiving, the Most Merciful. And that My torment is indeed the most painful torment.) 15:49-50, and

غَافِرِ الذَّنبِ وَقَابِلِ التَّوْبِ شَدِيدِ الْعِقَابِ

(The Forgiver of sin, the Acceptor of repentance, the Severe in punishment.) 40:3 and,

إِنَّ بَطْشَ رَبِّكَ لَشَدِيدٌ - إِنَّهُ هُوَ يُبْدِىءُ وَيُعِيدُ - وَهُوَ الْغَفُورُ الْوَدُودُ

(Verily, the punishment of your Lord is severe and painful. Verily, He it is Who begins and repeats. And He is Oft-Forgiving, full of love.)85:12-14. There are many other Ayat on this subject.