What is the meaning of "if they had entered it, they would not have exited it," and does that imply that obedience in sin is minor shirk that is not forgiven?

Ahl al-Sunnah (definition) are moderate in their dealings with perpetrators of major sins. They neither excommunicate them nor condemn them to eternal Hellfire. Rather, they believe that their fate is with Allah, unless their sin was shirk (definition). As for the texts that might suggest eternal Hellfire for perpetrators of major sins, they are interpreted in a way that aligns with the creed of Ahl al-Sunnah; for example, the text "If they entered it, they would not exit it until the Day of Judgment," is interpreted to mean the burning fire, or that "forever" means for the duration of this world. As for obedience in sin, if it involves making the unlawful lawful or the lawful unlawful, while knowing so, then it is major shirk. If it is due to personal whims without considering it lawful, then it is a sin requiring repentance. The perpetrator of minor shirk will not abide eternally in Hellfire, by agreement of Ahl al-Sunnah, but he may be punished for it unless he repents.