Muhammad ibn Hasan al-Mahdī (محمد بن الحسن المهدي), also known as Imam Zaman (Persian: امام زمان), is believed by Twelver Shī‘a Muslims to be the Mahdī, an eschatological redeemer of Islam and ultimate savior of humankind and the final Imām of the Twelve Imams who will emerge with Isa (Jesus Christ) in order to fulfill their mission of bringing peace and justice to the world. Twelver Shī‘a believe that al-Mahdī was born in 869 (15 Sha‘bān 255 AH) and assumed Imamate at 5 years of age following the killing of his father Hasan al-Askari.
Raj’at or Raj’ah الرَجعَة means the return to this life after death. This return will be during the government of Imam Al-Mahdi (AS) over the whole world. Allah will bring back to this world the best believers to witness the victory of Ahlul Bayt (AS). Allah will also bring back to this world the worst enemies of Islam to see that and get some of the results of their evil deeds.
Raj’ah is mentioned in Quran (Sura Ghaafir, verse 11).
Exegetes, Sunni and Shi'i, typically understand this verse to refer to the Day of Judgment.
Yawm, when used in this way in the Qur'an, typically refers to the Day of Judgment, as does the verb nab'ath (to resurrect from the dead).
The verses immediately before and after this one also appear to speak about the Day of Judgment; for instance, they speak of the Day when people submit directly to Allah (not a secondary agent, such as the Mahdi), and will see punishment directly from Allah (rather than through a secondary means, such as warfare, which is predicted to occur at the end times).
In this section, it also says that those who associated partners with Allah will see those partners, but this usually does not happen in this world, especially if those partners are non-physical beings such as angels or demigods, or intangible things like digital currency. However, after death, everything is made visible.
So the most likely interpretation is that the verse refers to the Day of Judgment.
Furthermore, to my recollection, narrations about the time of the Mahdi (A) on earth do not speak of witnesses coming from nations and presenting themselves for judgment. Instead, at that time, nations will split up: people will differ individually; some will follow him and some will not.
Rather, the Mahdi will be the witness over everyone since he will ultimately have rule over the planet, and (at least according to Shia belief) he has divinely granted knowledge about everyone.
As for why one witness is mentioned - Possibly, one witness is mentioned for each nation because a single witness will be able to bear witness to the nation as a whole. (On the topic of nations, here are some reflections by 'Allamah Tabataba'i about nations: https://www.al-islam.org/ask/what-have-ahlulbait-as-said-about-nationali...).
It is also narrated from Imam al-Sadiq (A) that every nation and every time has a witness; therefore, if each nation is different at a different time, it may have a witness for each time period. (For instance, Italy might have a witness for the pre-Roman period, the time of the ancient Roman Empire, the Christian Roman Empire, the modern nation-state of Italy, etc.; or those might be treated as different "nations".)
For the Muslim ummah, it is said that the witness is probably the Prophet (S) or the Imams (A), who would have access to knowledge of all the deeds of the nation. Some might argue that the witness is someone else who simply bears witness to the deeds, even if the Prophet and Imams are able to bear witness to all.
So, from all angles, the verse seems to speak about the Day of Judgment. However, as with many ayat of the Qur'an, the exact meaning of the ayah is open to interpretation, and sometimes the important thing is to ponder on what the meaning could be and see what one can take from it.
Aal Allah آل الله are in fact same as Aal Al-Rasool آل الرسول because Aal Al-Rasool are the pious Progeny of the Messenger whose obedience is obligatory on every Muslim being part and parcel of the obedience of the Prophet (SAWA) which is in fact the obedience of Allah (SWT).
Aal Allah are in fact Aal Al-Rasool as they are the Most obedient servants of Allah.
It means that people should not publicly claim to be in contact with Imam Mahdi (A) and use that as a grounds for their authority over people. It should also not be used as a justification for telling people what to do (for instance, telling people to change the shari'ah, or to give them money, or to follow a certain military leader, or to do anything else, because they say that this is what Imam Mahdi told them).
It is possible to meet Imam Mahdi (A) during the occultation and gain guidance or assistance, but this is a private matter, and it is between the individual and Allah whether or not that person truly met Imam Mahdi (A) or not.
No need to put the letter in a special box for protection and you can leave it bare with out cover and throw it in the water of river, see or well. It will be protected by Allah and will reach iA to Imam Al-Mahdi (AS).
There is no re birth but resurrections or return to this life which known as Raj'ah رجعة.
Raj'ah is the return of best servants of Allah and worst enemies of Allah to this life again to witness the victory of Islam and the punishment of its enemies. It is mentioned in Quran ( Sura Ghaafir, verse 11).
Imam Hussain (AS) will come back to this life in Raj'ah.
The 313 most trusted believers who will come with the Imam Al-Mahdi (AS) when he will come back to the public include many ladies. Some narrations mentioned that they will be fifty ladies among the 313. This is narrated by Jaabir Al-Jo'fi from Imam Al-Baqir (AS). (Ethbaat Al-Hodaat by al-Hurr Al-A'amily; 3:575.
In Dalaa'il Al-Imamah by al-Tabari , page 259: Mufadhdhal ibn Omar said: I heard Imam aal-Sadiq (AS) saying: There will be with The Imam Al-Qaa'im thirteen women. The narration says that the Imam Al-Sadiq (AS) mentioned some names of those ladies: Alqinwaa Bint Rasheed, Umm Ayman , Hubabah Al-Waalibiyyah, Sumayyah Umm Ammar, Zubaida, Umm Khalid Al-Ahmasiyyah, Um Sa'eed Al-Hanafiyyah, Subabah Al-Mashta, and Umm Khalid Al-Juhaniyyah.
So, the leading ladies with Imam Al-Mahdi (AS) are not just two but much more up to fifty. Thirteen of them will be very prominent personalities who will be resurrected from their graves to be with the Imam (AS).
You can put it is any will or water near your area. If there is no water at all, then you can burry it.
As the Abbasid government rulers' pressure on Imam Hasan Al-Askari (AS) and his family was tremendous, the disclosure of Imamate of Imam Mahdi (AS) was among the near circle of the most trusted persons. Imam Hasan Al-Askari (AS) told very few most trusted believers and allowed them to see his successor Imam Al-Mahdi (AS). These are names of some of those who saw Imam Al-Mahdi (AS):
1. Othman ibn Sa'eed Al-Amri who became later the first Safeer of the Imam Al-Mahdi (AS).
2. Muhammad ibn Othman ibn Sa'eed Al-Amri, who became later the second Safeer of the Imam.
3. Al-Husain ibn Rooh.
4. Ali ibn Muhammad Al-Samari.
5. Lady Hakimah daughter of Imam Al-Jawad (AS).
6. Ibraheem ibn Mahziyar Al-Ahwaazi.
7. Ahmad ibn Eshaq ibn Sa'd Al-Ash'ari.
8. Ahmad ibn Muhammad ibn Al-Mutahhar.
9. Ismael ibn Ali Al- Nawbakhti.
10. Ali ibn Ibraheem ibn Mahziyaar Al-Ahwaazi.
11.Kaamil ibn Ibrahim Al-Madani.
13. Muhammad ibn Ismael ibn Musa Al-Kadhim.
14. Al-Hasan ibn Wajnaa' Al-Naseebi.
15.Ibrahim ibn Idrees.
16. Ibrahim ibn A'bdah Al-kNisabori.
17.Ibrahim ibn Muhammad Al-Tabreezi.
18. Sa'ad ibn Abdullah ibn Abi Khalaf Al-Ash'ari.
19. Ali ibn Muhammad Al-Shimshaati.
20- Muhammad ibn Al-Qasim Al-Aqeeli.
There are hundreds of well known pious believers who saw Imam Al-Mahdi (AS). Whole books were been compiled on this subject by big scholars.
This is a very important question for those who really care to improve themselves and achieve better degrees of success in this life and hereafter. These are few practical steps which can make the believer more close to Imam-e-Zamana (AS). More piousness leads to more nearness to Imam-e-Zaman. To add to our Taqwa (Piousness), these are few points:
1. Asking yourself before any act or word whether Allah (SWT) likes it or not? That is the best degree of remembering Allah (SWT) along with continuous remembering him in our heart and tongue.
2. Reciting Quran and Du'a with understanding and pondering and gifting its reward to Imam Al-Mahdi (AS).
3. Performing Nawaafil prayers especially Night Prayer ( SALAT ALLAYL or NAMAZ E SHAB) every night.
4. Talking to Imam e Zaman (AS) every day and night as he listens to us and responds to the pious believers.
5. Gifting the reward of all our good deeds to Imam Al-Mahdi and all Ahlul Bayt (AS) which will not only multiply our reward, but also make us more near to them.
6. Having best Akhlaq (Manners) with parents, relatives especially your family members and with all people.
7. Being with Wudhu all the times as much as you can.
8. Trying to strengthen our will power by avoiding evil desires and performing good acts even if it can look like difficult like fasting, charity,etc. We need to control our desires and never allow our desires to control us.
9. Helping needy people in any possible way for the sake of Allah (SWT).
10. Trying to make believers happy by respecting them, caring for them, smiling in their faces and in any other act of generosity and kindness to them or their families.
11. Performing obligatory Prayers on time with out any delay. Imam Al-Mahdi (AS) performs every Prayer on time, so, your praying on time will make your Prayers elevated to Allah (SWT) with the Prayer of Imam Al-Mahdi (AS).
12. Keep your most important supplication and wish, the reappearance of Imam Al-Mahdi (AS) and sincerely pray for him more than praying for yourself and your family.
Anti Christ is a misleading person who will be killed by Al-Mahdi (AS). Jesus Christ (AS) will come down from the sky to this earth and will join Imam Al-Mahdi (AS) as one of his supporters and will pray behind him.
The government of Imam Al-Mahdi (AS) will last very long as we read in the narrations that: The rule of the Justice will long as much as the injustice ruled.
The person who claims such claim needs to read more about Imam Al-Mahdi (AS) who is the divine leader who will establish the world government of peace and justice for all human beings.
The Imam Al-Mahdi (AS) will have when he will re appear ten thousand sincere assistants who will lead and help people all over the world, out of them 313 will be the most pious and most sincere and most able to help the aim of the Imam (AS).
The 313 assistants will be regular individuals or scholars or leaders who have that high degree of sincerity and dedication to Allah (SWT). Many of them will be unknown to people because their sincerity stops them from seeking publicity, name or fame but known to Allah (SWT) as very humble and dedicated and pious. They will be men and women as well and from different parts of the world.