The Holy Prophet (pbuh) said:

يحِجُّ أغنِياءُ أُمّتي لِلنَّزهَةِ ويحِجُّ أَوسَاطُها لِلتّجارَةِ ويحِجُّ فُقَراؤُهُم لِلرّياءِ والسُّمعَةِ، فعِندَها يكُونُ أَقوامٌ يَتَعلّمُونَ القُرآنَ لِغيرِ اللهِ ويَتّخِذُونهُ مَزامِيرَ، ويكونُ أَقوامٌ يَتفقَّهونَ لِغيرِ اللهِ.

The rich will go to Mecca for amusement, the middle-class for business, and the poor for showing off and fame. At that time, people will learn the Holy Quran for purposes other than Allah, recite it as song, and engage in learning (Islamic) jurisprudence for worldly benefits.
See Tafsir al-Mizan; vol. 5 p.434 (as quoted from Tafsir al-Qummi)

The Holy Prophet (saw) says:

إنمَا فُرِضَتِ الصّلاةُ وأُمِر بِالحَجِّ والطّوافِ وأُشْعِرتِ المَناسِكُ لإقَامَةِ ذِكْرِ اللهِ، فإِذا لم يكُنْ في قَلبِكَ لِلمذكُورِ الّذي هو المَقصُودُ والمُبتَغى عَظَمَةٌ ولا هَيبَةٌ فَما قيمَةُ ذِكْرِك؟

The daily prayer, Hajj, circumambulation, and the other rites are aimed at remembering Allah. But when there is no remembrance of Him in your heart, what value will your oral remembrance have
See Jami'us-Sa'aadat; Vol. 3 p.322

Imam Sadiq (a.s) has said:

ورَأَيتَ بيتَ اللهِ قَد عُطِّلَ ويُؤمَرُ بتَرْكِهِ... فكُنْ على حَذَرٍ واطْلبْ إلى اللهِ النّجاةَ واعْلَم أنّ الناسَ في سَخَطِ اللهِ عزّ وجلّ...

(When) you see that Allah's House is closed down and the Hajj rites are abandoned, beware you; supplicate to Allah to be safe from His punishment, for people are at this time subject to Allah's wrath.
(See Rawzat ul-Kafi; vol. 8 p.37)

Imam Baqir (a.s) was quoted as saying:

إنَّ الحَاجَّ إذا أخَذَ في جِهازِهِ لم يَخطُ خُطْوَةً في شَيءٍ مِن جِهازِهِ إِلا كَتَبَ اللهُ عَزَّ وجَلَّ لهُ عَشْرَ حَسَناتٍ ومحَى عَنهُ عَشْرَ سَيّئاتٍ ورفعَ له عَشْرَ دَرَجَاتٍ حتّى يفْرُغَ مِن جِهازِهِ مَتى ما فَرَغ...

When a man intends to go on Hajj, for every step he takes in preparing for his journey Allah will write ten good deeds for him and will write off ten of his wrongdoings and will elevate his ten scales until he completes his preparatory affairs.
(See al-Kafi; Vol. 4)

Imam Sadiq (a.s) said:

الحُجَّاجُ يَصدُرونَ على ثَلاثةِ أصنافٍ؛ صِنفٌ يُعْتَقُ مِن النّارِ وَصِنْفٌ يَخْرُجُ من ذُنوبهِ كَهَيئَةِ يومِ وَلدَتهُ أُمُّهُ وصِنْفٌ يُحْفَظُ في أَهلِهِ ومَالِهِ، فَذلِكَ أَدْنى مَا يَرجِعُ به الحَاجُّ.

The Hajj pilgrims who return home are three groups; one are rescued from the fire (of Hell), another are cleansed from their sins as if they have been just born, and the third group return home with their wealth and family secured. This is the least reward the Hajj pilgrims can obtain.
(See al-Wafi; vol. 2 )

Imam Baqir (a.s) said:

الحَجُّ والعُمرَةُ سوقَانِ من أسواقِ الآخِرَةِ؛ اللازِمُ لهُما مِن أضْيافِ اللهِ تعالى. إِنْ أبقَاهُ، أبقاهُ وَلا ذَنبَ لهُ، وإنْ أَماتَهُ، أَدخَلَهُ الجَنّةَ.

Hajj and Umrah are two markets of the Hereafter. Those who enter into them are Allah's guests. If Allah preserves his guest's life, he will live free from sins and if He makes him die, he will be admitted into Paradise.
( See al-Wafi, Vol. 2)

Imam Sadiq (a.s) said:

الحَاجُّ والمُعتمِرُ وِفدُ اللهِ؛ إِن سَأَلوهُ أَعطَاهُم وإِن دَعَوهُ أَجابَهُم وإِن شَفَعوا شَفَّعَهُم وإِن سَكَتوا ابتَدَأَهُم ويَعوَّضُونَ بالدِّرهَمِ الفَ الفِ دِرهَم.

The performers of Hajj and umrah are Allah's guests. If they ask, they will be given, if they pray, they will be answered, if they intercede, their intercession will be accepted, if they keep silent, they will be blessed, and they will be given a million dirhams for each one they have spent.
See al-Wafi; Vol. 2

Imam Sadiq (a.s) said:

مَن نظَرَ الى الكَعبَةِ لم يَزَلْ تُكتَبُ لهُ حَسَنَةٌ وتُمحَى عنهُ سَيِّئَةٌ حَتّى يَنصَرفَ بَبَصَرِهِ عنهَا.

Whoever looks at the Kaaba, rewards are written for him and his wrongdoings are written off until he takes his look away from it.
See al-Kafi; Vol. 4

The Imam (a.s) also said:

مَن نظَرَ الى الكَعبَةِ كُتِبَتْ لهُ حَسَنَةٌ ومحِيَت عنهُ عشرُ سيّئاتٍ.

Whoever looks at the Kaaba, a reward is written for him and ten of his wrongdoings are written off.

Imam Sadiq (a.s) says:

إِنَّ للهِ تعَالى حَولَ الكَعبَةِ عِشرينَ ومِائَةَ رَحمَةً؛ منها سِتُّونَ للطّائِفِينَ وأَربَعون لِلمُصَلّينَ وعِشرونَ للنّاظِرينَ.

Allah sends down one hundred and twenty blessings in the precinct of the Kaaba; sixty for those who circumambulate, forty for those who worship and twenty for those who look at it.
See al-Kafi; Vol. 4

Addressing Imam Ali (a.s), the Holy Prophet (saw) says:

يا عليّ ، تارك الحجّ وهو مستطيع كافر ، يقول الله تبارك وتعالى : (وَلِلّهِ عَلَى النَّاسِ حِجُّ الْبَيْتِ مَنِ اسْتَطَاعَ إلَيْهِ سَبِيلاً وَمَنْ كَفَرَ فَإِنَّ اللهَ غَنِيٌّ عَنِ الْعَالَمِينَ) .يا عليّ ، مَن سوّف الحجّ حتّى يموت ، بعثه الله يوم القيامة يهوديّاً أو نصرانيّاً.

O Ali, one who forsakes Hajj while having the means (to perform it) is unbeliever, for Allah Himself has said: 'And pilgrimage to the House (Hajj) is incumbent upon men for the sake of Allah, upon everyone who is able to undertake the journey to it; and whoever disbelieves then surely Allah is Self-Sufficient above any need of the worlds.' O Ali, anyone who delays Hajj until he dies, Allah will raise him as Jew or Christian on the Day of Judgment.
See Men la Yahzuruh ul-Faqih; chapter: Miscellaneous matters

Imam Sadiq (a.s) says:

مَن مَاتَ وَلم يحِجَّ حِجَّةَ الإسلامِ؛ لم يمْنَعْهُ مِن ذَلِك حاجَةٌ تُجحِفُ بهِ أَو مَرضٌ لا يُطيقُ فيهِ الحَجَّ أَو سُلطانٌ يمنعُهُ فَلْيمُتْ يَهودِيّاً أو نَصرانِياً.

He who dies before he performs the obligatory Hajj while he was not too needy, too ill, or too persecuted to perform it will die as non-Muslim (i.e. Jewish or Christian).
See al-Kafi; vol. 4 p.268 Hadith 1.

Imam Ali (a.s) says:

فَرضَ اللهُ ... والحَجَّ تقوِيةً للدِّينِ.

Allah has made obligatory upon you the pilgrimage (Hajj), for it consolidates faith.
See Nahj ul-Balagha; saying 244

Imam Sadiq (a.s) says:

إِنَّ للهِ حُرُمَاتٍ ثلاثاً لَيسَ مِثْلَهُنَّ شَيٌء؛ كِتابُهُ وهُو نُورُهُ وحِكْمَتُهُ، وبَيتُهُ الّذِي جُعِل للنّاسِ قِبلَةً لا يقبَلُ اللهُ مِن أَحَدٍ تَوَجُّهاً الى غَيرِهِ، وعِترَةُ نَبيِّكُم محَمَّدٍ صَلّى اللهُ عليهِ وآلهِ.

Three things are sacred for Allah; His Book that is full of light and wisdom, His House that is the Kiblah towards which people offer their prayers and Allah does not accept from him who directs towards any other direction save the House-, and the Household the Holy Prophet (saw).
See Ibn Fettal an-Nishapuri's Eawdhat ul-Waizheen; 320

Imam Reza (a.s) said:

ومَا في ذلِكَ لجَمِيعِ الخَلقِ مِن المَنافِعِ... ومَنفَعةِ مَن في المَشرِقِ والمَغرِبِ ومَن في البَرِّ والبَحرِ ممَّن يحِجُّ وممِّن لا يحِجُّ من تاجِرٍ وجالبٍ وبائعٍ ومُشتَرٍ وكاسِبٍ ومِسكينٍ وقَضاءِ حوائِجِ أهلِ الأطرافِ...

The benefits of Hajj cover both east and west; those who perform the Hajj rites and those who do not whether they are businessmen, shopkeepers, or poor. People from all classes of societies are blessed with the benefits of Hajj.
See Elal ush-Shara'ie; vol. 2 p.90 Hadith 5

Imam Sadiq (a.s) says:

وَإِنَّ اللهَ لَيَدفَعُ بمَنْ يحِجُّ مِن شِيعَتِنا عَمَّن لا يحِجُّ منهُم، ولَو أَجمَعوا عَلى ترْكِ الحَجِّ لهلَكُوا.

Thanks to our Shiite pilgrims, Allah removes disaster from the Shiites who do not perform it, but if all agree to forsake Hajj, they will perish.
See Mustadrak ul-Wasail; Vol. 2 Section: Hajj p.4

Hajj Article Index