A wife is called the saha dharma charini in Sanskrit, which means the joint observer of the religious rites and ceremonies. The husband and the wife are considered to be one soul functioning in two bodies, one always helping and enriching the other.
A study of the human system tells that there are two systems of nerves in our body. The names can be mentioned as the cerebro-spinal system and the sympathetic system. The former consists of the nerves of the brain and the spinal cord, while the latter system regulates the bodily functions of organs such as circulation and respiration. In man, the cerebro-spinal system is fully developed while in a woman the sympathetic system is emphasized. For yoga and other ways of spiritual progress, the cerebro-spinal system is utilized whereas for the upkeep of the body the sympathetic system is important. In the absence of the former the latter would be non-existent and vice Versa. Hence one must nourish the other system. Generally, the cerebro-spinal system is considered to be more important than the sympathetic system. Hence it should be first taken care of. So a husband symbolizing the former system is nourished first and the wife is left what is not wanted for the husband to live upon.
The ordinary reason perhaps is that the husband by his practice of meditation and severe austerities has become a store house of magnetic force. While he is taking his meals, the plate or the leaf used with the food left in it is perhaps highly magnetized being saturated with his magnetism.
So by partaking of the food from the husband's leaf a wife absorbs into her system her husband's forcible magnetism and thus becomes purer. Further this magnetism if absorbed by other animals, might prove injurious to them, but a wife inured to her husband's magnetism would surely be the better for absorbing it into her system. This fact may be noticed in a family where the members are inured to the magnetism of the several members.