On what was assumed to be her deathbed, aged around 30 and suffering from a severe illness, she began to see visions of Jesus. The visions ended when she returned unexpectedly to health, but she wrote down a narrative version of the visions in a treatise known as the Short Text.
20 or 30 years later, she published the Long Text - a series of deeper, more detailed explorations of her visions. This text formed the basis for her most potent work: Revelations of Divine Love.
This book would have importance regardless of its content, for it is the first known published work in English by any woman. As it was, the 16 'lessons' within, taken from her visionary experience were to have huge influence on two branches of Christianity in particular - the Anglicans and the Lutherans.
The nature of her vision of Christianity was, for it's time, almost unique. Wheres many who lived at the time saw the constant recurring visitations of plague and famine as part of God's punishment for mankind's failings, her vision of God was far more optimistic and stressed a benevolent deity who would forgive sin.
Secondly, her approach to sin was more subtle than church teachings at the time. Whereas priests would excoriate sin from the pulpit and threaten eternal damnation for sinners, Julian argued that in fact that God had made humans fallible. Therefore, sin was inevitable and natural, and driven more by naivete than malice. In fact, it would be through sin that people would come to understand the kinds of hardships and pain and come to a deeper understanding of their place in God's nature.