THE MEANING OF HAJJ:
Linguistic meaning: An intended direction or destination.
Islamic meaning: Setting out to Al-Bait Al-Haraam in order to perform certain specific prescribed acts of worship in a particular prescribed period of time - for whoever is able to find a means to do it. Hajj is the fifth pillar of Islam which Allah has made obligatory upon every Muslim who meets three criteria: 1) past puberty, 2) sane and 3) possesses the (material) means to do it.
Al-Hajj Al-Mabroor: This the Hajj accepted by Allah Most High. It is the Hajj which was not contaminated by minor or major sins or any deviation.
Allah said:
وَأَتِمُّوا الْحَجَّ وَالْعُمْرَةَ لِلَّهِ فَإِنْ أُحْصِرْتُمْ ...
{Complete the Hajj and the Umra for Allah...} Al-Baqarah: 196
الْحَجُّ أَشْهُرٌ مَعْلُومَاتٌ فَمَنْ فَرَضَ فِيهِنَّ الْحَجَّ فَلَا رَفَثَ وَلَا فُسُوقَ وَلَا جِدَالَ فِي الْحَجِّ وَمَا تَفْعَلُوا مِنْ خَيْرٍ يَعْلَمْهُ اللَّهُ وَتَزَوَّدُوا فَإِنَّ خَيْرَ الزَّادِ التَّقْوَى وَاتَّقُونِ يَا أُولِي الْأَلْبَابِ (197)
{Hajj is specific known months so whoever intends therein to perform the Hajj, there is no sex or obscenity, no corrupt behaviour nor any arguing in the Hajj. And whatever good deeds you perform Allah knows them. And prepare your provision. The best provision is fear of Allah. Beware of Allah, O people of understanding.} Al-Baqarah: 197
The "known months" of the Hajj and they are the months which include all the actions of the Hajj, i.e., Shawwall, Dhu Al-Qi'da and the first ten days of Dhu Al-Hijja. You cannot make the ihraam of the Hajj outside of this period. Once you intend the Hajj, you are required to avoid all forms of disobedience to Allah Most High and even to avoid argumentation (which sinks to the level of personal attack) or other unpleasantries with the fellow Muslims.
{prepare your provision} Some of the Arabs used to say: "How is it that we visit Allah's house and He does not feed us?" They used to set out for the Hajj with no provision and say: "We are relying (tawakkul) on Allah." Allah orders us in this verse to take our provision with us to the Hajj. Especially to be sure to "take with us" taqwa of Allah - which is the best "provision" of Allah.
After mentioning that the Kaaba in Makka is the first house ever established solely for Allah Most High, He says:
فِيهِ آيَاتٌ بَيِّنَاتٌ مَقَامُ إِبْرَاهِيمَ وَمَنْ دَخَلَهُ كَانَ آمِنًا وَلِلَّهِ عَلَى النَّاسِ حِجُّ الْبَيْتِ مَنِ اسْتَطَاعَ إِلَيْهِ سَبِيلًا وَمَنْ كَفَرَ فَإِنَّ اللَّهَ غَنِيٌّ عَنِ الْعَالَمِينَ (97) قُلْ يَا أَهْلَ الْكِتَابِ لِمَ تَكْفُرُونَ بِآيَاتِ اللَّهِ وَاللَّهُ شَهِيدٌ عَلَى مَا تَعْمَلُونَ (98)
{In it are clear signs and the point where Ibrahim stood. And whoever enters it is in safety. And for Allah upon the people is the [obligation of] pilgrimage to the House - for all those who are capable of getting there. And whoever goes to kufr, surely Allah is free of any need for all of the peoples.} Aal 'Imraan: 97
Ibrahim was first ordered to call the people to the Hajj. Allah said:
وَأَذِّنْ فِي النَّاسِ بِالْحَجِّ يَأْتُوكَ رِجَالًا وَعَلَى كُلِّ ضَامِرٍ يَأْتِينَ مِنْ كُلِّ فَجٍّ عَمِيقٍ (27) لِيَشْهَدُوا مَنَافِعَ لَهُمْ وَيَذْكُرُوا اسْمَ اللَّهِ فِي أَيَّامٍ مَعْلُومَاتٍ عَلَى مَا رَزَقَهُمْ مِنْ بَهِيمَةِ الْأَنْعَامِ فَكُلُوا مِنْهَا وَأَطْعِمُوا الْبَائِسَ الْفَقِيرَ (28)
{And announce to the people the Hajj that they may come to you walking and on exhausted mounts coming from every deep valley. That they may see things beneficial to them and that they may remember the Name of Allah in certain prescribed days for the bounties We have provided them in herd animals. Eat from it and feed the poor and in difficulty.} Al-Hajj: 27-28
When Ibrahim complied with Allah's order in this verse and proclaimed the hajj to Makka, Allah caused his voice to be broadcast far and wide and all the people of the region received the announcement of the pilgrimage. In later days, the pilgrimage started by Ibrahim was perverted by the Arabs who had sunk into shirk and obscenity. Their worship during the pilgrimage consisted of "whistling and clapping" (as Allah described it) and making tawwaaf around the Kaaba stark naked!
Hajj is the fifth pillar of Islam. A pillar is that component without which the whole is not complete. Anyone who has the economic ability to make the Hajj or the means to obtain it and does not go, has failed in this pillar of Islam. That is why Allah mentions kufr right after mentioning that hajj is an obligation upon all those who have the ability. The Prophet (sas) said:
بُنِيَ الْإِسْلَامُ عَلَى خَمْسٍ شَهَادَةِ أَنْ لَا إِلَهَ إِلَّا اللَّهُ وَأَنَّ مُحَمَّدًا رَسُولُ اللَّهِ وَإِقَامِ الصَّلَاةِ وَإِيتَاءِ الزَّكَاةِ وَالْحَجِّ وَصَوْمِ رَمَضَانَ
"Islam is built upon five: 1) the testimony that there is no deity but Allah and that Muhammad is His Messenger, 2) establishing the prayer, 3) paying the Zakat, 4) pilgrimage to Allah's House and 5) fasting the month of Ramadhan." Muslim & Bukhari
Hajj is an obligation upon every Muslim who is able. This means that if you have not made the Hajj of your lifetime and must be given precedence over EVERY non-essential expenditure or trip.
A successful Hajj will cleanse one of ALL of their sins and give one a fresh start with Allah Most High. It is very important to try to maintain this state after returning from the Hajj. One of the signs of the last days is that people will become ignorant of this and will (from hadith):
مَنْ حَجَّ لِلَّهِ فَلَمْ يَرْفُثْ وَلَمْ يَفْسُقْ رَجَعَ كَيَوْمِ وَلَدَتْهُ أُمُّهُ
"Whoever performs the Hajj with no obscenity and no disobedience returns like the day his mother gave birth to him." Muslim & Bukhari
Performing the Hajj is the second best deed a Muslim can undertake coming after fighting in the path of Allah.
The Prophet (sas) was asked: "Which is the best of all deeds" and he (sas) answered: "Jihad in the path of Allah." Then it was said: "And then what?" To which he (sas) answered: "Hajj mabroor". Muslim & Bukhari
As mentioned previously, hajj mabroor mean a pilgrimage not contaminated by any obscenity, disobedience or deviation. The Prophet (sas) said about this kind of pilgrimage:
الْعُمْرَةُ إِلَى الْعُمْرَةِ كَفَّارَةٌ لِمَا بَيْنَهُمَا وَالْحَجُّ الْمَبْرُورُ لَيْسَ لَهُ جَزَاءٌ إِلَّا الْجَنَّةُ
"One Umra to the next is an expiation of all that is between them. As for Al-Hajj Al-Mabroor, there is no reward for it but Paradise." Muslim & Bukhari