And of the people is he who sells himself seeking means to the approval of Allah. And Allah is kind to the servants. (Al-Baqarah 207)
Translation,
Some people are such that they sell their lives in exchange for the pleasure and approval of Allah,

 And Allah, the Lord of Honor, is very kind to His servants,
This noble verse was revealed concerning the famous companion Hazrat Suhaib Rumi (may Allah be pleased with him). He was very wealthy, counted among the people of great families, used to wear expensive clothes, used to wear pairs worth hundreds of dirhams, but when he embraced Islam and intended to migrate, the disbelievers troubled him and started preventing him from migrating, and chased him out of Mecca. At that time, Hazrat Suhaib (may Allah be pleased with him) replied to the disbelievers that: "I am a skilled archer, it is difficult for you to compete with me, because as long as I have arrows and a bow, I will keep fighting, and then I also have a sword, I will not back down until the sword breaks, so don't even think about competing with me. Yes, if you want my wealth, want to seize all my property, then go, all my property is in such and such place, take it." The disbelievers were greedy for wealth, so Hazrat Suhaib (may Allah be pleased with him) referred the disbelievers to the greed for wealth, so they all left his way and went after seizing the wealth,
 Hazrat Suhaib Rumi (may Allah be pleased with him) migrated and came to Medina Pak, and met the Prophet (peace and blessings of Allah be upon him). The above-mentioned verse was revealed in his honor and praise,
After embracing Islam, such circumstances came upon him that he had nothing left and he became empty-handed. He told the whole story to the Prophet (peace and blessings of Allah be upon him). At that time, the Prophet (peace and blessings of Allah be upon him) said about him that
!Rabih al-Bay' Aba Yahya, Rabih al-Bay' Aba Yahya,
Your business and trade are profitable. 

The meaning of selling one's life and the standard of perfect faith 
ومن الناس من یشتری نفسہ ابتغاء مرضاۃ اللہ ،
And some people are such that they sell their lives in exchange for the pleasure and approval of Allah,
What is the meaning of selling one's self and life?
The meaning is to engage in obedience and compliance with Allah Almighty, just as a shopkeeper sells something, and then he has no authority or right to dispose of that item, in the same way, believers sell their lives for the pleasure of Allah and act according to the will of Allah, they do not take any step without His permission, which is against His will, and this is the standard of perfect faith which should be the attribute of all believers, Allah Almighty says,
ان اللہ اشتری من المؤمنین انفسھم واموالھم بان لھم الجنۃ, (At-Tawbah 111)
Indeed, Allah has bought from the Muslims their lives and their wealth in exchange for Paradise for them,

What is the meaning of Allah's kindness to His servants,
واللہ رؤوف بالعباد And Allah Almighty is very kind to His servants,
Allah Almighty's kindness to His servants is in the sense that: Allah grants him the ability to turn to Allah, grants him understanding and comprehension of religion, faith and the Holy Quran, not that whatever a servant wants, all his work is done,