For number one, another man’s words (unknown author) describe what it is and, what it means to me best:
A Mason is a man who professes a Faith in God. As a man of Faith, he uses the tools of Moral and Ethical Truths to serve mankind.
A Mason binds himself to the like-minded men in a brotherhood that transcends all religious, ethnic, social, cultural, and educational differences.
In Fellowship with his brothers, a Mason finds ways in which to serve his God, his family, his fellow man, and his country.
A Mason is dedicated. He recognizes his responsibility for Justice, Truth, Charity, Enlightenment, Freedom, Liberty, Honesty and Integrity in all aspects of human endeavour.
A MASON IS ALL THIS AND MORE
Number two, I presume you mean after the time that Speculative members were added to the fraternity (of course prior, it was primarily a stone workers guild). I believe the fundamentals listed in answer one above were largely the historical reasons we have developed beyond that of the guild. The driving force to become more and to serve a higher cause.
Number three, is also largely answered above. The majority of other fraternities encircle a close bond of like fellows without necessarily a definitive goal beyond always recognizing each other first. The Masons go far beyond any other fraternity in that we seek to serve a noble cause. Those causes are so well outlined above...for me.