Significance of Caturmasya

The Cāturmāsya period begins in the month of Āsādha (June-July) from the day of Ekādaśī called Śayanā-ekādaśī, in the fortnight of the waxing moon. The period ends in the month of Kārtika (October-November) on the Ekādaśī day known as Utthānā-ekādaśī, in the fortnight of the waxing moon. This four-month period is known as Cāturmāsya.
Some Vaisnavas also observe it from the full-moon day of Āsādha until the full-moon day of Kārtika. That is also a period of four months. This period, calculated by the lunar months, is called Cāturmāsya, but others also observe Cāturmāsya according to the solar month from Śrāvana to Kārtika. The whole period, either lunar or solar, takes place during the rainy season.
Cāturmāsya should be observed by all sections of the population. It does not matter whether one is a grhastha or a sannyāsī. The observance is obligatory for all āśramas.
The real purpose behind the vow taken during these four months is to minimize the quantity of sense gratification. This is not very difficult. In the month of Śrāvana one should not eat spinach, in the month of Bhādra one should not eat yogurt, and in the month of Āśvina one should not drink milk. One should not eat fish or other nonvegetarian food during the month of Kārtika.
A nonvegetarian diet means fish and meat. Similarly, masūra dāl and urad dāl are also considered nonvegetarian. These two dāls contain a great amount of protein, and food rich in protein is considered nonvegetarian. On the whole, during the four-month period of Cāturmāsya one should practice giving up all food intended for sense enjoyment.

What is Caturmasya?

Chaturmasya is an auspicious four-month period starting from Ashadha Shukla Dashami to Kartika Shukla Paurnima. The months of Shravana, Bhadrapada, Ashvina and Kartika fall under this period. These four months are said to be very pleasing to Bhagavan Vishnu.
There is an interesting conversation between the Varaha form of Lord Vishnu and Dharani Devi occuring in the Varaha Purana about the significance of this Chaturmasya period.
Once Dharani Devi, concerned about the people who take birth in the Kali Yuga who are ignorant, short lived and always afflicted with ailments, approached Lord Varaha and pleaded Him to reveal the method in which even the people of Kali Yuga get great benefits even with very little effort.

Sri Varaha smilingly replied – There is a 4 month period in a year known as Chaturmasya wherein any Dana, Vrata, Japa and Homa performed brings forth countless merits. Compared to the noble deeds performed during other months, those performed in these holy months, would no doubt, yield multifold benefits.
On hearing this, Dharani Devi asked. O Lord, why among the 12 months only these 4 months are so auspicious?
To this Lord Varaha replied – In an year, the 6 months beginning from Ashadha are called Dakshinayana. 6 months beginning from Pushya are termed as Uttarayana. This period of one year for human beings is equivalent to 1 whole day(day/night) for the celestials (Devas). Pushya to Ashadha is the day and Ashadha to Pushya is the night for the Devas.
Once, I was sitting on the top of the Meru mountain. At that time, all the celestials approached and said – “O Lord – currently it is night for us. So, we would take leave of you.
Then a lady dark in complexion wearing white sparkling clothes holding parashu in her hand came forward, prostrated and spoke to Lord Varaha – O Lord, I am ratri who is the abhimanini of this part of the year. I am sad that during this time, no auspicious events like Marriage etc take place. All people dislike me and term be as be ing inauspicious. There is not point in continuing my life like this. I would like to end my life unable to bear this insult. I can only live if you bless me”.
All the devas also prayed – “Oh Lord! Kindly show mercy on Ratri whereby she will become happy”.
Heeding to the prayer of all the Devas Lord Varaha granted boon to Ratri devi.
Lord Varaha spoke – “Oh Ratri, you have three Yamas(1 Yama = 4th part of night or 2 months). Out of these three yamas the first two yamas (4 months i.e Chaturmasya) would henceforth become dearer to me. Any pious deed performed during these two Yamas (Chaturmasya) brings forth immense merits.  Among these four months of Shravana, Bhadrapada, Ashvina, Kartika, the merits accrued would increase day by day. That is the reason why the last Month, Kartika is most beneficial in all respects. Hearing this, Ratri Devi became very happy and returned to her abode".
Lord Varaha continued - "Oh Dharani, that time onwards, this chaturmasya period became very dear to me. I benevolently grant great merits to anyone who performs noble deeds like Snana, Dana, Vrata, Homa, Japa during this period”. 
Chaturmasya is also a period in which Lord Narayana enters into Yoga-Nidra. This does not mean that Lord Narayana sleeps like us mortals. Even, the demi-gods are called Animishas because they have no sleep. What to speak of Lord Narayana, the creator of all these demi-gods? Therefore, this is to be understood to be just another playful sport of the Almighty.
The Lord is the presiding deity for all the four months with his Sridhara, Hrishikesha, Padmanabha and Damodara forms respectively.

The four vratas in Chaturmasya 
During the four months period, certain food items are prohibited. The respective vrata is named after the item that is prohibited during the month. So, the names of the four vratas are
1. Shaka Vrata
2. Ksheera Vrata
3. Dadhi Vrata
4. Dvidala Vrata 

Who are eligible to do this Chaturmasya Vrata?
 This Vrata can be performed by one and all. There is no discrimination based on age/gender/caste/ashrama. Brahmanas, Kshatriyas, Vyshyas, Shudras, Women, Grihasthas, Sanyasins are all eligible to undertake this vrata.
If one does not undertake this vrata due to ignorance or negligence, he would surely thrown into the hell for a long time. 

Shaka Vrata(Ashadha-Shukla-Ekadashi to Shravana-Shukla-Dashami):
Shaka Vrata, is the first of the four Vratas of Chaturmasya. As the very name indicates, Shaka or any kind of Vegetable and fruit should not be offered to Lord nor should be partaken.
The following list gives what can be used during this Vrata
1. All pulses
2. Jaggery
3. Oils
4. Milk/Curds 
The following list gives what is not to be used during this Vrata
1. All fruits (incl. mango)
2. All Vegetables
3. All leafy-vegetables, curry-leaves, kotambri
4. Lemons
5. Spices - Cashew, Dry Grapes etc.
6. Tamarind

Dadhi Vrata (Shravana-Shukla-Ekadashi to Bhadrapada-Shukla-Dashami)
In this second Vrata curds/yogurt is disallowed.
Ksheera vratha (Bhadrapada-Shukla-Ekadashi to Ashvina-Shukla-Dashami)
Milk and all its derivatives are disallowed,
Dvidala vratha (Ashvina-Shukla-Ekadashi to Kartika-Shukla-Dashami)

All pulses, which have two halves like channa, toor, masoor, urad, groundnuts are disallowed..
Health is given importance during the four months. Many people avoid garlic and onion as it can stimulate unnecessary excitements, cause indigestion and distract devotee from pujas and prayers. In some regions, people avoid green leafy vegetables in the Shravan month. Curd, or yoghurt, is avoided in Bhadrapad, milk is avoided in Ashwin month and pulses, the split variety, are avoided in Kartik month.

Once, on being asked by Narad about the proper methods of performing Shodash upachar rituals, lord Brahma said –’In normal circumstances, when lord Vishnu is worshipped by employing the rituals of Shodashopachar it is considered as ‘Tapa’. But, when the same rituals of shodashopachar are employed to worship lord Vishnu during chaturmas, it is considered as ‘Mahatapa’. In the same manner, all the austerities that are observed during Chaturmas attain greater importance.

Most of the important festivals associated with Hinduism are closely linked to agriculture and especially the harvest season. The monsoon rains brings joy, greenery and fresh air and the four months is considered highly auspicious and ideal for rituals, pujas and festivals.
The first month in Chaturmas, Shravan is dedicated to Lord Shiva, especially the Mondays. The next month is Bhadrapad, the month of festivals including the Ganesh Chaturthi and Krishna Ashtami. Then comes Ashwin month and the important festivals include, Durga Puja, Navratri, Diwali etc. Finally, Kartik, Diwali celebrations end in this month.
People take different vows during Chaturmas – some people avoid non-vegetarian food, some decide to read the Mahabharata or Ramayana or Bhagavad Gita or the Bhagavad Purana on all days, some make it a point to visit temples on all days, some decide to chant a prayer or mantra daily ‘x’ number of times.