Two divisions of sastra—smarta and paramartha
The Vedic arya-sastras are divided into two sections—smarta (literature based on smrti) andparamartha (transcendental literature based onsruti). Those who are eligible (adhikari) for thesmarta section do not have any natural inclination or taste for the paramartha-sastras. The thoughts, principles, activities and life goal of every human is constituted according to his respectiveruci (inclination). Generally, smartas accept those scriptures which are in accordance with their respective ruci. Having greater adhikara forsmarta-sastra, they do not demonstrate much regard for paramarthika-sastra. Providence is the agent behind the creation of these two divisions. Therefore, undoubtedly the maintainer of the world must have a hidden purpose in having made such an arrangement.
As far as I understand, the purpose is that the jivas sequentially make progress in their level of consciousness by remaining steadfast in their respective adhikara. By deviating from one’s adhikara, one falls down. According to one’s activities, a person attains two types of adhikara—karmadhikara and bhakti-adhikhara. As long as one maintains hiskarmadhikara, he derives benefit from the path shown by the smarta section. When he enters bhakti-adhikara, by transgressing the karmadhikara, then he develops a natural ruci (inclination) for the paramarthika, or transcendental, path. Therefore, providence has made these two divisions of sastra: smarta and paramartha.
The rules and regulations of smarta sastra are committed to karma
The smarta sastra has made various types of rules and regulations in order to help one attain nistha, steadfastness, in karmadhikara. In many instances, it even demonstrates indifference towards paramartha sastra to make people attain specific nistha in such rules and regulations. In reality, although sastra is one, it manifests in two ways for the people. If the jiva gives up adhikara-nistha, he can never attain auspiciousness. For this reason, the sastras have been divided into two: smarta and paramartha.
Adhimasa (extra month), also called mala masa (impure month), is devoid of all auspicious activities
By dividing the whole year in twelve parts, the smarta-sastras have ascertained the auspicious, or religious, activities for these twelve months. All the karma, religious activities which are part of the varnasrama system when allotted to the twelve months, leave the extra month (adhimasa) devoid of any such activity. There is no religious performance in adhimasa. In order to keep lunar months and solar months in tally, one month has to be excluded every 32 months. The name of that month is adhimasa(extra month).* Smartas have discarded this extra month, considering it abominable. They gave it names such as mala masa (impure month), cora masa (thieving month), and so on.
* It is stated in Sri Surya Siddhanta that in one mahayuga there are 1,593,336 extra months and 51,840,000 solar months. Therefore, there is one extra month after every 32 months, 16 days and 4 hours of the solar calendar.