The meaning of the Hadith 'All of them will be in Hellfire except one'

Q 3: What is meant by the Hadith of the Prophet (peace be upon him) concerning the Ummah (nation) in which he said: ...all of them will be in Hellfire except one (sect). Which one? Will the other seventy-two sects abide in Hellfire forever as is the ruling on the Mushrik (one who associates others with Allah in His Divinity or worship)? (Part No. 2; Page No. 231)  When we say “the Ummah of the Prophet (peace be upon him),” does that refer to those who follow him and those who do not follow him?

A: The Ummah meant in this Hadith is Ummah Al-Ijabah (the Ummah which has accepted the Prophet’s Call to Islam) and it will divide into seventy-three sects: seventy-two of them are deviant sects that introduced Bid‘ahs (innovations into the religion) that do not put them beyond the pale of Islam. They will be punished in Hellfire for their deviation and invented practices except those whom Allah pardons and forgives. Their end will be in Paradise. The one saved sect will be Ahl-ul-Sunnah wal-Jama`ah (adherents to the Sunnah and the Muslim mainstream) who abided by the Sunnah of the Prophet (peace be upon him) and remained adhering to the very same way of the Prophet (peace be upon him) and his Companions (may Allah be pleased with them) in all affairs. The Prophet (peace be upon him) said about them: A group among my Ummah will continue to follow the truth and to be victorious, and they will not be harmed by those who forsake them or oppose them, until the Command of Allah comes to pass. As to those whom their Bid‘ahs put them beyond the pale of Islam, they fall under Ummah Al-Da‘wah (the Ummah which is called to Islam) and not among the Ummah which accepted Islam; they will be punished by dwelling in Hellfire forever, which is the preponderant scholarly opinion. Another opinion holds that that the meant Ummah in this Hadith is Ummah Al-Da‘wah, which includes each and everyone to whom the Prophet (peace be upon him) was sent: those who believed as well as those who disbelieved him. Consequently, the one excluded is Ummah Al-Ijabah, which exclusively refers to those who truly believed in the Prophet (peace be upon him) and remained so until they died, and it is the meant “saved sect” from Hellfire, either to be rescued from it without being punished at all or after being punished and then they will be admitted to Paradise. (Part No. 2; Page No. 232) As for the other seventy-two sects, excluding the one saved sect, they are all disbelievers who will abide in Hellfire forever.Thus, it becomes clear that “Ummah Al-Da‘wah” is a more general and inclusive term than “Ummah Al-Ijabah” who accepted Da‘wah (the Call to Islam) and believed in Allah and in His Messenger. Anyone who accepted Islam and became one of Ummah Al-Ijabah is also one of Ummah Al-Da‘wah, but not everyone in Ummah Al-Da‘wah (i.e., not everyone who is called to Islam) is also one of Ummah Al-Ijabah (i.e., accepted Islam and became one of the Muslim Ummah).May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.