Allah's statement,

وَكَذَلِكَ فَتَنَّا بَعْضَهُم بِبَعْضٍ ...

Thus We have tried some of them with others!

means, We tested, tried and checked them with each other,

... لِّيَقُولواْ أَهَـؤُلاء مَنَّ اللّهُ عَلَيْهِم مِّن بَيْنِنَا ...

That they might say: "Is it these (poor believers) that Allah has favored from amongst us!''

This is because at first, most of those who followed the Messenger of Allah were the weak among the people, men, women, slaves, and only a few chiefs or noted men followed him.

Nuh, was also addressed by his people مَا نَرَاكَ إِلاَّ بَشَرًا مِّثْلَنَا وَمَا نَرَاكَ اتَّبَعَكَ إِلاَّ الَّذِينَ هُمْ أَرَاذِلُنَا بَادِيَ الرَّأْيِ (Nor do we see any follow you but the meekest among us and they (too) followed you without thinking). (11:27)

Heraclius, emperor of Rome, asked Abu Sufyan, "Do the noblemen or the weak among people follow him (Muhammad)?''

Abu Sufyan replied, "Rather the weak among them.''

Heraclius commented, "Such is the case with followers of the Messengers.''

The idolators of Quraysh used to mock the weak among them who believed in the Prophet and they even tortured some of them. They used to say, "Are these the ones whom Allah favored above us,'' meaning, Allah would not guide these people, instead of us, to all that is good, if indeed what they embraced is good.

Allah mentioned similar statements in the Qur'an from the disbelievers,

لَوْ كَانَ خَيْراً مَّا سَبَقُونَآ إِلَيْهِ

Had it been a good thing, they (weak and poor) would not have preceded us to it! (46:11)

and,

وَإِذَا تُتْلَى عَلَيْهِمْ ءَايَـتُنَا بِيِّنَـتٍ قَالَ الَّذِينَ كَفَرُواْ لِلَّذِينَ ءَامَنُواْ أَىُّ الْفَرِيقَيْنِ خَيْرٌ مَّقَاماً وَأَحْسَنُ نَدِيّاً

And when Our clear verses are recited to them, those who disbelieve say to those who believe: "Which of the two groups is best in position and station.'' (19:73)

Allah said in reply,

وَكَمْ أَهْلَكْنَا قَبْلَهُمْ مِّن قَرْنٍ هُمْ أَحْسَنُ أَثَاثاً وَرِءْياً

And how many a generation (past nations) have We destroyed before them, who were better in wealth, goods and outward appearance. (19:74)

Here, Allah answered the disbelievers when they said,

...أَهَـؤُلاء مَنَّ اللّهُ عَلَيْهِم مِّن بَيْنِنَا أَلَيْسَ اللّهُ بِأَعْلَمَ بِالشَّاكِرِينَ ﴿٥٣﴾

"Is it these (poor believers) that Allah has favored from amongst us!'' Does not Allah know best those who are grateful!

Meaning is not Allah more knowledgeable of those who thank and appreciate Him in statement, action and heart!

Thus Allah directs these believers to the ways of peace, transfers them from darkness to light by His leave, and guides them to the straight path.

In another Ayah, Allah said;

وَالَّذِينَ جَـهَدُواْ فِينَا لَنَهْدِيَنَّهُمْ سُبُلَنَا وَإِنَّ اللَّهَ لَمَعَ الْمُحْسِنِينَ

As for those who strive hard for Us (Our cause), We will surely guide them to Our paths (i.e. Allah's religion). And verily, Allah is with the doers of good.'' (29:69)

An authentic Hadith states,

إِنَّ اللهَ لَا يَنْظُرُ إِلَى صُوَرِكُمْ وَلَا إِلَى أَلْوَانِكُمْ، وَلَكِنْ يَنْظُرُ إِلَى قُلُوبِكُمْ وَأَعْمَالِكُم

Allah does not look at your shapes or colors, but He looks at your heart and actions.