Nobody knows where this tradition started from. According to Hinduism, it is considered as the oldest tradition, for a wife to serve a glass of milk to her husband on their wedding night.
Wives want their husbands to be in good health. Milk is considered as the source of protein. Once you add crushed almonds to milk, it provides protein at a higher rate that eventually improves the hormone rate.
While it may seem silly to the modern woman, in previous generations, brides and grooms didn't know each other. So this glass of milk may have been an ice breaker of sorts.
