The Auspicious Month of Kartika
The month of Kartika is the last month of the rainy season called Caturmastya. The Caturmasya period begins in the month of Asadha (June-July) from the day of Ekadasi called Sayana-ekadashi, in the fortnight of the waxing moon. The period ends in the month of Kartika (October-November ) on the Ekadasi day known as Utthana ekadasi, in the fortnight of the waxing moon. This four month period is known as Caturmasya. Some vaisnavas also observe it from the full moon day of Asadha util the full moon day of Kartika. That is also a period of four months. This period, calculated by the lunar months , is called Caturmasya, but others also observe Caturmasya according to the solar month from Sravana to Kartika. The whole period, either lunar or solar, takes place during the rainy season.
Caturmasya should be observed by all sections of the population. It does not matter whether one is grihastha or a sannyasi.The observance is obligatory for all asramas. 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 Sravana one should not eat spinach, in the month of Bhadra one should not eat yogurt, and in the month of Asvina one should not drink milk. One should not eat fish or other non-vegaetarina food during the nonth of Kartika. A non- vegetarian diet means fish and meat. Similarly , masura dhal and urad dhal are also considerd non-vegetarina . The two dhals contain a great amount of protein, and food rich in protein is considerd non-vegetarin. On the whole, during the four-nonth period of Caturmasya one should practice giving up all food intended for sense enjoyment.
[Sri Caitanya caritamrta, Madhay-lila 4.169 purport]
The execution of devotional service during Urja vrata in the month of Kartika is especially recommended to be performed at Mathura. This system is still followed by many devotees. They go to Mathura or Vrndavana and stay there during the month of Kartika specifically to perform devotional services during this period.
In the Padma Purana it is said , the lord may offer liberation or material happiness to a devotee , but after some devotional service has been executed, particularly in Mathura during the month of Kartila, the devotees want only to attain pure devotional service unto the Lord.
The purport is that the lord does not award devotional service to ordinary persons who are not serious about it. But even such unserious person who execute devotional service according to the regulative principles during the month of Kartika, and within the jurisdiction of Mathura in India, are very easily awarde the Lord's personal service (Nectar of Devotion, Chapter 12)