I have noticed that when a person converts from one religion to Islam it is said that he or she reverted. This is said even when it is the first time he or she embraces Islam as a religion. Why is this?
In Islam, we have a concept called mithaaq, which means "heavy covenant/contract." According to this understanding, all of humanity met Allah (God) before we were created, and we agreed to follow His rules.
Therefore, we all have a fitrah (innate nature) to the values of Islam, because we are all born as Muslims.
More specifically, this can be extracted from the narration of our prophet (peace be upon him):
No [child] is born but upon Fitra (natural inclination to Islam). It is his parents who make him a Jew or a Christian or a Polytheist. A person said: Allah's Messenger, what is your opinion if they were to die before that (before reaching the age of adolescence when they can distinguish between right and wrong)? He said: It is Allah alone Who knows what they would be doing.
Source: Saheeh Muslim
Good question. The origin of the term comes from something the Prophet Muhammad (saws) said about everyone being born "on their nature" (the word used in the hadith is "fitrah"). Meaning that people are born with an innate ability to recognize their Lord and to submit to Him. The hadith continues by saying that after birth, it is the parents who make the child a Christian, Jew or Magian. So the people who like to use the term "revert" say that when one recognizes Allah as their Lord, they revert to their original state at birth.
I personally avoid using the term because a Muslim is something that someone is consciously, something that they believe in from their own intellect, something that they say and act upon. This is not the same state as a newborn baby.
To cover the opinion side of this question, temporarily without citations, let me tell you what I know of this personally. Though logic should count for something right?
The first time I heard of this was after telling another Muslim that I dont feel like I changed my religion as much as I have simply increased my knowledge of religion. The term better characterizes this feeling then convert. After all, I truly desired to be a Muslim by definition when I was Christian, so I didnt necessarily feel like I changed my religion. I still believed in One God as a Christian.
Alot of people I've met say the same thing. Eventually I'll find people saying the same thing in quotable formats and I'll start adding references to this to back up my statement. God willing.
The other funny thing is, just to highlight the ideal, that I dont really see other Christians as being non Muslims. People care about the prophet Jesus, the Bible, church, the pope, etc because of a simple belief in a Creator who Sustains and Provides for us every day.
In my own case I try to avoid the whole question of 'revert' versus 'convert'. Pretty much every day in my time in Saudi Arabia I was asked if I was a Muslim. In answer I stated the Shahada in English in a very serious wholehearted way: "There is one Allah, and Mohammed is His prophet". I have never recited this in Arabic, because I know neither the language nor Arab culture from many centuries ago. In contrast I can be very clear when I say this in English. So for most questioners this satisfied them, but not all. Interestingly, my Muslim academic colleagues from Europe, who also taught at my university, were the least satisfied! So for me this statement of the Shahada is completely true for me, and also in no way excludes the pearl of truth at the heart of many if not all religions. To me this statement of faith on the biggest issues is far more important, than any business of categorising or identifying myself as a 'convert' or 'revert'. It's all a question of priorities. Let the others judge! Let others risk the sin of TAKFIR accusing another Muslim of not being a Muslim!