Muslims commemorate the fortieth day after the martyrdom of Imam Hussain (AS) and his companions, called Arbaeen, meaning the fortieth day in Arabic. They all gather around the city of Karbala and Imam Hussain’s (AS) shrine, mourning and lamenting the unfair and cruel war between his comrades and those of Yazid Ibn Muawiyah, which led into the death of those pure men and the bondage of their families. 

This commemoration happens every year around the city of Karbala. Muslims begin to walk to Karbala from other towns. They gather together in groups to pray, and especially to mourn the martyrdom of Imam Hussain (AS).
This walk is a hard one. It takes at least three days and lots of energy and time. So, why do Muslims take that? What is the philosophy behind it? 

To answer our questions, first, let’s have a review of the history behind this walk and then move to the other aspects of this commemoration. 

1. What is the Arbaeen Walk?

The history of Arbaeen walk goes back to the first visitors of Imam Hussain (AS) after his death. On the day of Arbaeen, forty days after the tragic martyrdom of Imam Hussain (AS), Imam’s (AS) son, sister and the remaining members of his family and that of the other martyrs came back to Karbala to lament the death of their dear ones besides their graves.  

Their next visitor was Jabir Ibn Abdullah Ansari on the year 61 AH. Visiting Imam Hussain’s (AS) shrine was a tradition in Shiite culture until a short period after Morteza Anasari’s became the religious reference (Marja’) of Shiite Muslims. It was then lessened for some years and then revived. Some other religious references (Marja’) kept this tradition alive among their followers, until the government of Saddam Hussain, which banned all religious Shiite traditions to be performed publically [1]. 

The tradition was revived after the fall of Saddam, and it is still to be continued. 

2. Why on Foot?

Visiting the holy shrines and going on pilgrimages on foot is not something new or belonging to our age. It’s got a long history, and Adam did the first pilgrimage on his visit to Mecca [2]. It isn’t a tradition just among Muslims either. It is performed in other faiths and religions, too. For instance, Caesar made a vow to his God to go on a pilgrimage to the Dome of Rocks if he won the battle against the Empire of Persepolis (Iran). He performed his vow after his victory [3].

Pilgrimages are highly admired, and their act is seen as a way of getting closer to Allah by Imam Sadiq (AS). Visiting the holy shrines of the twelve Imams (AS) is even more praised, especially the sacred shrine of Imam Hussain (AS). Of course, it’s not these shrines themselves that are of value and importance, but the people who have been buried there. Thus, when one makes a pilgrimage toward these shrines, he/she finds the chance to think more about these great personalities who won Allah’s satisfaction and praise and were Muslims in the real sense of the word. So, in every step that a pilgrimage takes toward Imams' (AS) shrines, especially that of Imam Hussain (AS), he/she is getting closer to a source of spiritual blessing, bringing him/her thousands of virtues and wiping away thousands of vices from his/her mind and soul.

3. What is the Philosophy behind the Arbaeen Walk?

The Arbaeen pilgrimage is not merely a long walk. Instead, it is a kind of movement in which despite being in publics, pilgrims have their own private relationship with Allah and Imam Hussain (AS), which finds a new form of divine immaterial dependence and conformance. Thinking about the goals and the history behind the martyrdom of Imam Hussain (AS), the injustice and cruelty imposed on his family and the devotions of his faithful followers brings about many personal and social growth and improvements. 

Meeting other Muslims, exchanging ideas, and making friendships with Muslims of the other countries is another social outcome of this pilgrimage. One finds out that they are not alone in their faith, and have friends all over the world. They may have differences, but they have one thing in common: Belief in Imam Hussain (AS) and his right cause. 

The last and the most crucial point to mention this great gathering is it's a kind of preparation for the grand reappearance of Imam Mahdi (AS), the awaited savior among Muslims. The Arbaeen pilgrimage is to make the minds and souls ready for this great event. It is said that when Imam Mahdi (AS) reappears, he introduces himself as the son of Hussain (AS) [6], whose fame has reached many people through the Arbaeen Pilgrimage; one of the most significant religious gathering around the world, with the estimated number of 40,000,000 people participating in it, whose news is broadcasted all over the world [5].  

References

1. "The background of Arba'een rally/The importance of Najaf-Karbala rally from the scholar's viewpoint." Fars News. Archived from the original on 16 November 2015. Retrieved 4 October 2015.
2. Hor Ameli, Muhammad Bin Hussain Vasayel-o-Shia, Vol 11, p 132
3. Sobhani, Jafar The Light of Eternity p. 696
4. Kamel-o-Ziyarat: Pp 183, 184 and 185
5. Philipson, Alice (19 January 2015). "The ten largest gatherings in human history." The Telegraph. Archived from the original on 6 October 2015. Retrieved 3 October 2015. 
6. Khademi Shirazi, Mohammad Yad’e Mahdi P16, P132

Lady Zainab (SA) is an icon of purity, bravery, and steadfastness.Though she lived 14 centuries ago, her personality and teachings continue to guide men and women till now/to this day. She is the fruit of the tree of Prophethood nourished by Imamat. Lady Zainab (SA), the daughter of Imam Ali (As), has several attributes and titles associated with her, such as Al-Aqilah the noblewoman, Al-Aalimah or the knowledgeable woman and Aminatu-al-Allah, the faithful of Allah (SWT).
She belonged to a holy lineage; her mother was Lady Fatimah al-Zahra (SA), - the daughter of Prophet Muhammad (PBUH & HP) - and was actually a reflection of her father in the worship of Allah, piety, self-discipline, virtues, clemency, veneration, and the other features of perfection thus her father named her the chief of the women of the worlds and such a great mother nurtured Lady Zainab. 

Lady Zainab’s life

Lady Zainab’s father, Imam Ali (AS) honoured as the representative, successor and heir to Prophet Muhammad (PBUH&HP) was given remarkable titles like ‘the chief of the prophets’ successors’, ‘leader of the pious ones’ and ‘the head of the worshippers’ by Prophet Muhammad (PBUH&HP) himself.  With innumerable merits and unrivalled sacrifices for Islam he was recognised and reputed as the most knowledgeable, the most magnanimous, the most generous, the most abstinent, the most trustworthy, the best worshipper, the most faithful, and above all, the most pious and the bravest of all Muslims. In other words, he was the best Muslim after the Holy Prophet Muhammad. (PBUH&HP).

Lady Zainab  (SA), hence, was  born into the most pious family and raised  under the care of the best human beings therefore she learnt many things that composed her perfect personality from the etiquettes of her parents and her brothers.  Since early life, she was marvellous in her intellect and wisdom and had learnt the Holy Quran by heart as well as the Prophet’s sayings regarding Islamic laws, rules of education and principles of ethics.

Throughout her life she faced one tribulation after another, but emerged strong and victorious in all her trials. She then witnessed the martyrdom of her mother, father and brothers - Imam Hasan and Imam Hussain (AS) - and in Karbala where all male members of her family were brutally martyred including her own sons Awn and Muhammad, and all the women folk were taken into captivity. But despite all these vicissitudes she always remained a source of strength and a caretaker for the survivors of the tragedy of Karbala and the flagbearer of the message of this great event. She is the epitome of selflessness and perseverance, the embodiment of patience and courage in the face of oppressors and the personification of knowledge and purity. Despite all the hardships she endured in Karbala she decided to preserve and propagate the true message of Karbala While her bravery, eloquence, courage, asceticism, chastity and caring nature towards the survivors of the tragedy of Karbala has been and still is unparalleled in history. 

The Holy Prophet Muhammad (PBUH&HP) says, “Whoever tries to fulfil the needs of a sick person, whether they fulfil it or not, they will be cleansed of their sins like the day they were born.”[1] In another tradition,   he has said, “Whoever looks after the sick for an entire day, Allah (SWT) will raise them up with Prophet Abraham.”[2] If we would take only these two traditions into consideration, we can understand the greatness of Lady Zainab (SA) who cared for Imam Sajjad (AS) and all the children and women who had got sick or were injured after what happened in Karbala. Therefore, taking inspiration from her, the 5th of Jamadi-Al-Awwal which is her birthday is celebrated as the Nurses’ Day in the Islamic calendar. 

References:

1.  Kitab Man La Yahzarul Faqih, V.4, Pg.16 
2.   Sawab ul Aamal, Pg. 341
3.    https://www.al-islam.org/lady-zaynab-badr-shahin/life-lady-zaynab 
4.  https://www.al-islam.org/victory-truth-life-zaynab-bint-ali-muna-haeri-bilgrami