In Pushti Marg, Shri Yamunaji occupies the most important position as the "beloved of Shri Nathji". She is the very embodiment of divine grace. Shrimada Vallabhacharyaji gained his first darshan of the Lord through Her grace.
Daughter of the Lord Surya (Sun) and sister of Lord Yama (God of death), the goddess is said to have come down from the heavens to bless the world.
Ganges is the goddess of action, Sarasvati is the Goddess of knowledge and Yamunaji is the goddess of bhakti - devotion. Hence, it was only right that She should be chosen as the patron goddess of Pushti Marg which relies so heavily on divine grace and bhakti.