A friend ask me to explain the last sentence, here we go..
//"It is not easy to be a believer because he need to put himself as a specimen to be an integral part of his own experiment in which he is an observer too."//
The word Momin signifies knowledge based on conviction from his own personal experience. The status of a Momin is greater than those who are educated by reading someone's else book or hearing somebody's else experience. To become a Momin one has to become a specimen by putting himself on the aperture of the microscope and experience / observe the experiment he is undertaking upon himself.
The faith, trust, security he achieve by experimenting upon himself is far greater than all the qualification he could acquire through theoretical knowledge.
Hence Momin is a person who is self aware or self conscious and self taught by experimenting on himself. A Momin is more secure, feel more safe, more confident because his trust, faith and conviction is far greater due to the virtue of acquiring wisdom and knowledge by undergoing through the experiment upon himself.
Usually people think believer is blind follower but in terms of the book Quran when the word Momin occurs it means he is not a blind follower. The author of the book is addressing those believers who have [shahadah] witnessed / seen / experienced the entire ayaat [signs] by themselves.
If you have not witnessed, observed, experienced Allah and Rasul in your life time then you are not a Momin according to the term momin of the book Quran and your utterance of witness [Kalimah Shahdah] is a BIG LIE.