The Hypocrites fear Public Exposure of Their Secrets
Allah tells;
يَحْذَرُ الْمُنَافِقُونَ أَن تُنَزَّلَ عَلَيْهِمْ سُورَةٌ تُنَبِّيُهُمْ بِمَا فِي قُلُوبِهِم
The hypocrites fear lest a Surah should be revealed about them, showing them what is in their hearts.
Mujahid said,
"The hypocrites would say something to each other then declare, `We wish that Allah does not expose this secret of ours,"
There is a similar Ayah to this one, that is, Allah's statement,
وَإِذَا جَأءُوكَ حَيَّوْكَ بِمَا لَمْ يُحَيِّكَ بِهِ اللَّهُ وَيَقُولُونَ فِى أَنفُسِهِمْ لَوْلَا يُعَذِّبُنَا اللَّهُ بِمَا نَقُولُ حَسْبُهُمْ جَهَنَّمُ يَصْلَوْنَهَا فَبِيْسَ الْمَصِيرُ
And when they come to you, they greet you with a greeting wherewith Allah greets you not, and say within themselves;"Why should Allah punish us not for what we say!"
Hell will be sufficient for them; they will burn therein. And worst indeed is that destination! (58;8)
Allah said in this Ayah,
قُلِ اسْتَهْزِوُواْ إِنَّ اللّهَ مُخْرِجٌ مَّا تَحْذَرُونَ
Say;"(Go ahead and) mock! But certainly Allah will bring to light all that you fear."
He will expose and explain your reality to His Messenger through revelation.
Allah said in other Ayat,
أَمْ حَسِبَ الَّذِينَ فِى قُلُوبِهِمْ مَّرَضٌ أَن لَّن يُخْرِجَ اللَّهُ أَضْغَـنَهُمْ
وَلَوْ نَشَأءُ لَارَيْنَـكَهُمْ فَلَعَرَفْتَهُم بِسِيمَـهُمْ وَلَتَعْرِفَنَّهُمْ فِى لَحْنِ الْقَوْلِ
Or do those in whose hearts is a disease, think that Allah will not expose their ill-wills?
Had We so willed, We could have shown them clearly to you, so that you would know them by their marks; but you will know them by the tone of their speech! (47;29-30)
This is why, according to Qatadah, this Surah is called `Al-Fadihah' (the Exposing), because it exposed the hypocrites