Question 40: What is the reason for Hajj, and what is its purpose?
Answer: In short, Hajj in Islam the attendance at a specific time of the year, in a specific place which is the sacred house of Allah or the Kaaba. So first we must know the attribute of the time and place.
Question 39: Why was the army of Abraha al-Habashi stoned when it wanted to demolish the Kaaba with shale rocks, and the Ummayyad army was not when they wanted to demolish the Kaaba to the point where the catapult fell in the Kaaba and demolished the sacred house?
he sun is the Messenger of Allah pbuhap, the moon is Imam Ali pbuh , and the planet is Imam Al-Mahdi pbuh. 
The sun, moon, and planet in the Kingdom of Heaven were the manifestation of Allah in the creation. For this reason, they were made similar to Abraham pbuh and each of these three is a manifestation to its own extent. And Muhammad, Ali and Al-Qaim pbut, specifically, are the complete manifestation of Allah in the creation in this world. This is because not only are they dispatched, but they are dispatchers as well.
And he said to me: come behind me and I shall make you circle [the Kaa’ba]. So my wife and I went behind him and he made us circle the Kaa’ba (Tawaf Al-Hajj/The Circling of Pilgrimage), and we did not feel any crowd or narrowness [of space], and he was reading Dua’s and Dhikr (invocations), and from them was Dua’ Kumayl, and I was sending a lot of peace and blessings upon Muhammad and the Family of Muhammad ([making a lot of Salawat]), and I was saying within myself: perhaps this is The Mahdi Muhammad son of Al-Hassan (pbuh), but I would say: who am I that the Mahdi may come [especially] for me and make me circle [the Kaa’ba]?!
The Ka’ba or the Sacred House of Allah is but a manifestation on Earth of the House of Allah that was placed in the Kingdom of Heavens so as the angels may circumambulate it imploring Allah’s forgiveness for contesting Him regarding His vicegerent Adam (a.s).