We know what the 5 pillars of Islam are, but Allah demands Iman in all of the Quran (and not in parts of it) from everyone - be they born Muslims, Jews, Christians, Sabians, or from any other religion. But the situation is critical as far as born Muslims are concerned because they are under the impression that they have Iman by virtue of their birth. Most Muslims are, in fact, Muslims because they were born in Muslim families, so much so, that a person born in a Sunni family is considered Sunni just as a person born in a Shia family is considered Shia. If they were born in Hindu, Jewish or Christian families, they will be Hindus, Jews, or Christians, respectively. In view of the prevalent belief systems then, how can a born Muslim justify his/her Iman in light of the Quran? Remember that if a person did not have the freedom to choose something, he/she is not responsible for it. So, if we (born Muslims) did not freely and consciously choose Islam, we are not entitled to it in an active sense but only in a passive sense.
Originally, all the Sahaba (R) had accepted Islam with due thought and understanding and therefore, they were among the category of true Quranic mu’mins. However, many tribes accepted Islam in masses when Islam had become well-established as a system with rule of law in society. The Quran refers to these people as follows:

"These bedouins say that they are mu’mins. O Prophet! Tell them that you do not have Iman. You have only accepted to surrender (to Islam). Iman has not yet entered your hearts." (49:14)

The meaning and aspects of Iman from the Quran which sheds light as to why these bedouins should not call themselves mu’mins. If Allah does not let these bedouins call themselves mu’mins, who willingly accepted to enter Islam, how can born Muslims call themselves mu’mins, who did not accept Islam by choice and did not fulfill the requirements of Iman?