وَرَبَطْنَا عَلَى قُلُوبِهِمْ إِذْ قَامُوا فَقَالُوا رَبُّنَا رَبُّ السَّمَاوَاتِ وَالاَْرْضِ

And We made their hearts firm and strong when they stood up and said:"Our Lord is the Lord of the heavens and the earth,

Here Allah is saying:`We gave them the patience to go against their people and their city, and to leave behind the life of luxury and ease that they had been living.'

Several of the earlier and later Tafsir scholars have mentioned that;

they were sons of the kings and leaders of Byzantium, and that they went out one day to one of the festivals of their people. They used to gather once a year outside the city, and they would worship idols and offer sacrifices to them. They had an arrogant, tyrannical king who was called Decianus, who commanded and encouraged the people to do that. When the people went out to attend this gathering, these young men went out with their fathers and their people, and when they saw their people's actions with clear insight, they realized that the prostrations and sacrifices the people were offering to their idols should only be dedicated to Allah, Who created the heavens and the earth.

Each of them started to withdraw from his people and keep aloof from them. The first one of them to move away on his own went and sat in the shade of a tree, then another came and sat with him, then another came and sat with them, then four more followed suit one by one. None of them knew the others, but they were brought together by the One Who instilled faith in their hearts.

As it says in the Hadith recorded by Al-Bukhari with an incomplete chain of narrators from A'ishah (may Allah be pleased with her), the Messenger of Allah said:

الاَْرْوَاحُ جُنُودٌ مُجَنَّدَةٌ فَمَا تَعَارَفَ مِنْهَا ايْتَلَفَ وَمَا تَنَاكَرَ مِنْهَا اخْتَلَف

Souls are like recruited soldiers. Those that recognize one another will come together, and those that do not recognize one another will turn away from each another.

Muslim also recorded this in his Sahih from the Hadith of Suhayl from his father from Abu Hurayrah from the Messenger of Allah.

People say that similar qualities or characteristics are what bring people together. So each of the young men was trying to conceal what he really believed from the others, out of fear of them, not knowing that they were like him.

Then one of them said, "O people, you know by Allah that only one thing is making you leave your people and isolate yourselves from them, so let each one of you say what it is in his case."

Another said, "As for me, by Allah I saw what my people are doing and I realized that it was false, and that the only One Who deserves to be worshipped Alone with out partner or associate is Allah Who created everything, the heavens, the earth and everything in between."

Another said, "By Allah, the same thing happened to me."

The others said the same, and they all agreed and became brothers in faith. They adopted a particular location as a place of worship and began worshipping Allah there, but their people found out about them and told their king about them. The king ordered them to appear before him, and asked them about their beliefs. They told him the truth and called him to Allah, as Allah says about them:

وَرَبَطْنَا عَلَى قُلُوبِهِمْ إِذْ قَامُوا فَقَالُوا رَبُّنَا رَبُّ السَّمَاوَاتِ وَالاَْرْضِ لَن نَّدْعُوَ مِن دُونِهِ إِلَهًا

And We made their hearts firm and strong when they stood up and said:"Our Lord is the Lord of the heavens and the earth, never shall we call upon any god other than Him..."

"Never" (Lan) implies an absolute and eternal negation, meaning, `this will never happen, and if we were to do that it would be false.'

So Allah says about them:
 
لَقَدْ قُلْنَا إِذًا شَطَطًا
 
 
if we did, we should indeed have uttered an enormity in disbelief.

meaning, untruth and utter falsehood