In numerous traditions, it is stated that the term BaqiyatAllah in verse 86 of Surah Hud is a reference to the person of Imam Mahdi (A.S) or some of the other Imams (A.S). For example, the book IkmÁl al-Din narrates the following from Imam Baqir (A.S): The first words which the Mahdi (A.S) will speak after his rise will be this verse: “‘What remains of Allah’s provision is better for you, should you be faithful…”He will then say: I am the BaqiyatAllah and his proof and his caliph amongst you. After that, no one will greet him except that he will say: Peace be upon you oh BaqiyatAllah Fe Arzeh. ( اَلسَّلامُ عَلَیْکَ یا بَقِیَّةَ اللّهِ فِی أَرْضِه )
In regards to the verses of the Qur’an, it is true that while a verse may have been revealed in regards to a specific situation, it can also pertain in a general sense to other issues as well. This can extend and apply even in to other centuries in regards to various issues which are general in nature. It is correct that the aforementioned verse is specifically referring to the people of Shuaayb and the term BaqiyatAllah is referring to lawful divine benefit; yet at the same time, anything or anyone that is beneficial from God can also be considered as BaqiyatAllah. All of the prophets and divine leaders are a form of BaqiyatAllah. All of the truthful leaders who fight against the enemies of humanity can be considered as a form of BaqiyatAllah, this similarly applies to the soldiers and fighters who strive in such a path.
Since Imam Mahdi (A.S) is the last leader and his battle will be the final revolution in the history of mankind, it makes sense that the term BaqiyatAllah applies to him and he is indeed worthy of such a title. In addition, he is what remains of the Prophet (PBUH) and the rest of the Imams (A.S).