Teresa was brought up as a Christian by parents who were converts from Judaism.They had worked hard to assimilate into Spanish Christian culture because of her paternal grandfather's condemnation as a denier of the faith and one who returned to Judaism.Teresa found great comfort and inspiration in the stories of the martyrs and greatly desired to imitate their lives. At the age of nineteen, she left her family and joined the local Carmelite monastery as a nun. Teresa knew sin well. In fact, she spoke about it passionately as a subject she had received divine inspiration on. She described sin in terms of estrangement and alienation from God. Teresa, the one who said "It is love alone that gives worth to all things," knew that sin was essentially a lack of life-giving love, mercy, and grace. However, Teresa was best known for her ecstatic and mystical moments. She had visions and felt that the way to union with God was through love and through self-abnegation and resignation. She taught first that to find God we must begin by focusing on our own failures with a penitent and contemplative heart. She called this part of the ascent of the soul to God "heart's devotion."
The second stage of the ascent of the soul to God through the self is called the "devotion of peace." In this, God delivers a state of spiritual peace upon the person as they continue to meditate upon love, grace, and mercy knowing that they cannot save themselves but that salvation is assured to those who trust in God. This peace does not mean the destruction of distraction but only that the person is becoming closer to God and being helped along the journey toward God by God's prevenient grace. Memory, reason, and imagination are still humanly focused.
The third stage of the ascent of the soul to God is called the "devotion of union." In this state, the reason of the person becomes subsumed by God's will and the person becomes further united with God and, therefore, less united with sin. As they walk the path of love that leads to God--and God alone--they find that sin has less of a hold on their life. As they give more of themselves over to God, they find that it rests securely in God. In this stage of mystical union with God, the soul begins to rest comfortably in the overwhelming love of God.
Finally, the soul ascends to the "devotion of ecstasy." In this place of prayer, the soul divests itself of all that is self and becomes intimately associated with God who is Love. Teresa described this state as being a type of sweet and happy pain. The person is changed and sin is ripped from them as they no longer have a place where it can dwell. Of course, they must again return to the world as we know it but their momentary intimacy with God has fortified them and strengthened their growing faith. In many ways, this was the essence of Teresa's teaching. There was hope for escape from sin but only in providing less room for it to dwell. Ultimately, sin was only destroyed by the soul's ascension to God and the incubation of love within the heart.