Milk in general symbolises the Fitratul Islam and the Sunnah of Rasoolullah (Sallallaahu-alayhi-wasallam). Fitratual Islam means the natural religion of Islam while Sunnah means the actions of RAsoolullah (Sallallaahu-alayhi-wasallam). Thus, dirnking or possessing milk suggest that the observer will attain righteousness and he will remain stead fast on his Deen.