قُلْ أَنزَلَهُ الَّذِي يَعْلَمُ السِّرَّ فِي السَّمَاوَاتِ وَالاَْرْضِ
Say;"It has been sent down by Him Who knows the secret of the heavens and the earth."
meaning, He has revealed the Qur'an which includes true information about the earlier and later generations, information which concurs with the realities of the past and future.
الَّذِي يَعْلَمُ السِّرَّ
(Who knows the secret),
means, Allah is the One Who knows the unseen in the heavens and on the earth; He knows their secrets just as He knows what is visible therein.
إِنَّهُ كَانَ غَفُورًا رَّحِيمًا
Truly, He is Oft-Forgiving, Most Merciful.
This is an invitation to them to repent and turn back to Allah, telling them that His mercy is vast and His patience is immense. Whoever repents to Him, He accepts his repentance. Despite all their lies, immorality, falsehood, disbelief and stubbornness, and saying what they said about the Messenger and the Qur'an, He still invites them to repent and give up their sin, and to come to Islam and true guidance.
This is like the Ayat;
لَّقَدْ كَفَرَ الَّذِينَ قَالُواْ إِنَّ اللَّهَ ثَـلِثُ ثَلَـثَةٍ وَمَا مِنْ إِلَـهٍ إِلاَّ إِلَـهٌ وَحِدٌ وَإِن لَّمْ يَنتَهُواْ عَمَّا يَقُولُونَ لَيَمَسَّنَّ الَّذِينَ كَفَرُواْ مِنْهُمْ عَذَابٌ أَلِيمٌ
أَفَلَ يَتُوبُونَ إِلَى اللَّهِ وَيَسْتَغْفِرُونَهُ وَاللَّهُ غَفُورٌ رَّحِيمٌ
Surely, disbelievers are those who said;"Allah is the third of the three."
But there is no god but One God. And if they cease not from what they say, verily, a painful torment will befall on the disbelievers among them.
Will they not turn with repentance to Allah and ask His forgiveness! For Allah is Oft-Forgiving, Most Merciful. (5;73-74)
إِنَّ الَّذِينَ فَتَنُواْ الْمُوْمِنِينَ وَالْمُوْمِنَـتِ ثُمَّ لَمْ يَتُوبُواْ فَلَهُمْ عَذَابُ جَهَنَّمَ وَلَهُمْ عَذَابُ الْحَرِيقِ
Verily, those who put into trial the believing men and believing women, and then do not turn in repentance, then they will have the torment of Hell, and they will have the punishment of the burning Fire. (85;10)
Al-Hasan Al-Basri said;
"Look at this kindness and generosity! They killed His friends and He is calling them to repentance and mercy.