قُلْ يَجْمَعُ بَيْنَنَا رَبُّنَا
...
Say: "Our Lord will assemble us all together..."
means, `on the Day of Resurrection, He will bring all of creation together in one arena, then He will judge between us with truth, i.e., with justice.'
...
ثُمَّ يَفْتَحُ بَيْنَنَا بِالْحَقِّ
...
then He will judge between us with truth.
Each person will be rewarded or punished according to his deeds; if they are good, then his end will be good, and if they are bad, then his end will be bad. On that Day they will know who has attained victory, glory and eternal happiness, as Allah says:
وَيَوْمَ تَقُومُ السَّاعَةُ يَوْمَيِذٍ يَتَفَرَّقُونَ
فَأَمَّا الَّذِينَ ءَامَنُواْ وَعَمِلُواْ الصَّـلِحَـتِ فَهُمْ فِى رَوْضَةٍ يُحْبَرُونَ
وَأَمَّا الَّذِينَ كَفَرُواْ وَكَذَّبُواْ بِـَايَـتِنَا وَلِقَأءِ الاَّخِرَةِ فَأُوْلَـيِكَ فِى الْعَذَابِ مُحْضَرُونَ
And on the Day when the Hour will be established -- that Day shall (all men) be separated. Then as for those who believed and did righteous good deeds, such shall be honored and made to enjoy luxurious life (forever) in a Garden of Delight. And as for those who disbelieved and denied Our Ayat, and the meeting of the Hereafter, such shall be brought forth to the torment. (30:14-16)
Allah says:
...
وَهُوَ الْفَتَّاحُ الْعَلِيمُ
And He is the Just Judge, the All-Knower of the true state of affairs.