All of these are mottos or slogans that are typical symbols used in dystopian fiction. Just as in Huxley's Brave New World and Orwell's 1984, Ayn Rand's novella takes place in a future following an upheaval in which the old world (now "unmentionable") has been swept away in what is considered a Rebirth or Revolution, and the population is now living under an unfree and mind-controlling system. The "Great Truth" functions like the three principles of INGSOC in 1984, expressing the ideology of the dictatorship of the future. In Rand's dystopia the leaders regard as evil ones anybody who tries or tried to reestablish individuality and the previous values of society before the cataclysm occurred that led to the dystopia.

The Uncharted Forest represents a physical analogue to the forbidden ideas the regime suppresses. Often in dystopian fiction there still exists a remnant of the old, pre-dystopian world, though unlike in Anthem, in other novels that remnant is still easily accessible, such as the neighborhoods of the proles in 1984 and the "Savage Reservation" in Brave New World. It is generally through a discovery of that old-world vestige that the protagonists come to understand that the leadership has created a dysfunctional society that enslaves people and destroys them.

Anthem is Ayn Rand's paean against collectivism, and it champions Rand's philosophy -- the ultimate in individualism -- called objectivism.  The Great Truth, then, in this society that pushes collectivist principles to the extreme in order to show their flaws, is that there are no individuals, only the collective.  Only the collective has value.  The Unmentionable Times refers to the time before the Great Rebirth, the time when individuals were privileged and the good of the collective was sacrificed to individuals' selfish desires before society realized the Great Truth of collectivism.  It was during the Unmentionable Times that people knew and used the word "I" to refer to themselves instead of "we".  The Evil Ones are those people who fought then or still fight against the collective and insist on the importance of the individual.