Hajj is one of the five main pillars of Islam. The Prophet (peace and blessings be upon him) said, “Islam is built upon five pillars: testifying that there is no true god except Allah and that Muhammad is the Messenger of Allah, performing Prayer, paying the Zakah, making the pilgrimage to the Sacred House (Hajj), and fasting the month of Ramadan.” (Al-Bukhari)
On the significance of Hajj, the prominent Muslim scholar Sheikh Yusuf Al-Qaradawi says,

There are many wisdoms behind Hajj. Among these wisdoms is the wisdom that Almighty Allah prepares man to have the perfect form of servitude to Him. There are many acts of Hajj whose significance man cannot conceive by his limited intellectual powers. However, a Muslim accepts these acts and fulfills them out of his obedience and surrender to Almighty Allah. For instance, one may ask himself the following questions: Why Tawaf (Circumambulation around Ka`bah)? Why should it be in 7 rounds, not 3 or 5? What is the significance of throwing pebbles? And why 7 pebbles in particular? Why staying at or standing on `Arafah? Why and why…?
All these endless questions may intrigue one’s mind, but the clear fact is that their answers are beyond man’s limited faculty, and only what he is required to say is: I hear and obey Your Command, O Allah! Yours is to order and mine is to obey”!
Islam lays emphasis on the very principle of equality between all people. It makes it clear that people are as equal as the comb teeth. The Prophet (peace and blessings be upon him) declares:“O people! Your Lord is One, your father is one. You are all sons of Adam and Adam is created from dust.” In prayer, a person may wear his own traditional costumes and thus may be distinguished. In Hajj, it is totally different as all people put on two pieces of white cloth that resemble a shroud. This is the highest form of equality.
In Hajj, man enters into a state of total sanctity that prevents him from violating the life or the safety of any human being. Hajj is the sign of the universality of this Divine message. All people come from all parts of the globe celebrating the praises of the One true God, no colors, races, regional borders. All barriers are removed, and all pilgrims are molten in one brotherhood that gathers their hearts and strengthens their bonds and sense of belonging to one religion.
hajj is, above all, a revolution against all usual matters. A person who travels for Hajj may be traveling out of his country for the first time. Moreover, he experiences a life that is simple but happy. All these are among the benefits of Hajj about which we are told in the Qur’an. In the Hereafter, the benefit is greater; it isParadise. The Prophet (peace and blessings be upon him) says: “He who performs Hajj and avoids sin and vice in it, will return as sin free as the day his mother bore him.” In another Hadith, the Prophet (peace and blessings be upon him) declares: “An accepted Hajj is rewarded with nothing more than Paradise.”

Shedding more light on the ethics and significance of Hajj, Ibn Qudamah Al-Maqdisi says in his book Mukhtasar Minhaj Al-Qasidin:

One who intends to perform Hajj should first make Tawbah (repentance to Allah), settle his debts, prepare sufficient provision for his journey and for his family until his return, give back trusts to their rightful owners, and meet his expenses by lawful means. He is recommended to accompany righteous men to help each other in their journey. If there is a group of people going out for Hajj, they should choose one of them to be their leader during their journey so as to set their affairs in order.
the pilgrim should stick to the Islamic good manners in all aspects, ask righteous people to make Du`aa’ (supplication to Allah) for him, and say the authentic Prophetic supplications that the Prophet (peace and blessings be upon him) is reported to have said on his journey and making Hajj. These Prophetic supplications are dealt with in detail in the books of Fiqh, so one should refer to them for more information in this regard.
You should get yourself well-acquainted with the fact that there is no way of drawing to Allah, Most High, except by divesting oneself of desires, abstaining from pleasures, confining oneself to necessities and devoting oneself exclusively to Allah, Most High, in every moment and rest. It was for this reason that the ascetics of previous religions used to isolate themselves from the people, retiring to mountain caves and preferring solitude to the company of others, in quest of intimacy with Allah, Most High.
hajj, therefore, is decreed by Allah to be the ascetic act of the Muslim Ummah. The pilgrim is recommended to free his minds from all businesses except the obedience of Allah, Most High. He should be shabbily dressed, and disheveled, keeping away from adornment or inclining to things that excite vainglory and rivalry.
here, we may recall the narration of Jabir (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: “Allah, Most High, boasts before the angels about the pilgrims, saying, ‘Look at My servants; they came to Me, disheveled and dusty, from every deep ravine. I make you witness that I have forgiven them.'” (Ibn Khayzamah)
allah, Most High, has honored His House, sanctified it, and made it a visiting-place.
You should, furthermore, know that every action and pillar pertinent to Hajj comprises a lesson or an admonition to people of sound mind as follows:
When the pilgrim feels himself impelled to take a lot, seeking enough provision to last him the whole journey without spoiling or going bad before he reaches his destination, let him remember that the journey to the Hereafter is much longer and that the provision for it is true piety. Apart from piety, whatever one supposes to be provision will be left behind one’s death, leaving him in the lurch. Beware, therefore, from spoiling your deeds, which make up your provision for the Hereafter, by the taint of hypocrisy and showing-off.
It is recommended for the pilgrim, on departing his homeland, to remember the assured departure of this transitory world to the Hereafter.
On putting off his normal clothes and wearing the clothes of Ihram, he should recall the shroud in which he will be wrapped for burial.
as the pilgrim utters the words of Talbiyah, he should bear in mind that this signifies a response to the summons of Allah, Most High, as it is stated in the Qur’anic verse that reads, (And proclaim the pilgrimage among men: they will come to thee on foot and (mounted) on every kind of camel, lean on account of journeys through deep and distant mountain highways) (Al-Hajj 21: 27).
On entering the Haram (the Sacred Precinct), he should be filled with hope of being spared the Punishment of Allah, Most High, and on beholding the Ka`bah, the pilgrim should be conscious in his heart of the majesty of the House, venerating it with such intensity that he seems to anticipate beholding the Lord of the House. He, further, should express his gratitude to Allah, Most High, for bringing him to this high degree, and for including him in the company of those who draw near to Him.
On touching the Black Stone, the pilgrim should believe that he is pledging allegiance to Allah, Most High, and vowing obedience to Him. He, also, has to make his resolve to be loyal to his oath, for the wrath of Allah is the traitor’s due.
Clinging to the coverings of the Ka`bah and pressing one’s breast against its wall (at the part called Al-Multazam), the pilgrim’s intention should be to draw close in love and yearning to the House and the Lord of the House, seeking grace through the contact and hoping for immunity from the Hell-Fire. At the same time, his intention should be earnestly to seek forgiveness and to beg for mercy, just as one who has sinned against another will cling to his clothes while imploring his pardon, demonstrating that he has no refuge or recourse except to his forgiveness.
Going between Safa and Marwah, the pilgrim should recall how he will oscillate between the two scales of the Balance at the site of Resurrection. Also, he demonstrates devotion to duty and hopes to be viewed with compassion, just like who enters the presence of a king and leaves without knowing whether the sovereign has decided to accept or to reject him. He keeps going back across the courtyard time after time, hoping to receive mercy the second time if not the first.
On standing at `Arafah, the pilgrim should – when he beholds the thronging crowds, hears the loud voices speaking in many tongues, and sees the various groups following their Imams through the ritual observances – recall the site of Resurrection, the gathering of the communities with their Prophets and leaders, each community following its Prophet, aspiring after the intercession, all wavering with equal uncertainty between rejection and acceptance.
as for throwing the pebbles, the pilgrim’s purpose in this should be obedience to the Divine command, to demonstrate submissiveness and servitude and readiness to comply without any obvious rational of psychological justification.
When the pilgrim’s eyes behold the wall of Madinah, he should remember that this is the town which Allah, Most High, chose for His Prophet (peace and blessings be upon him) that he made it the goal of his migration, that this was his home. He should further envisage the footprints of the Messenger of Allah (peace and blessings be upon him) as he went about the city and recall how he used to go about its streets, picturing to yourself his humility and his graceful gait.
On visiting Allah’s Messenger, the pilgrim should feel in his heart his tremendous dignity and realize that he is aware of his presence, of his visit, and that he is receiving his greeting. The pilgrim, also, should imagine the noble form of the Prophet (peace and blessings be upon him).
all the aforementioned points serve as ethics to which every pilgrim should pay attention on embarking on this noble and lifetime journey.