"Once Upon a Time": Religious Symbolism
Like Lucifer, Regina, was once a symbol of innocence and beauty. However when her mother killed her True Love Daniel, Regina chooses revenge, a sin, over forgivness.
The Evil Queen convinces Snow White to eat the apple by making her believe it is her only option. This is a mirror of what Satan does with Eve in the garden of Eden. People commonly believe that the fruit of knowledge that Eve eats is an apple. The show and the Grimm's fairy tale, Snow White, use a poison apple to portray the consequences of sin. Snow is only resurrected by True Love's kiss (God).
Later in the series Regina becomes increasingly aware that her relationship with Henry is not good and she is loosing him. Henry decides to move in with Emma and his grandparents. In an attempt at winning Henry back Regina begins a journey to becoming good. She has a few slip ups but over time she is able to be good. Once she fully embraces this role she realises it is her only chance of a happy ending (heaven) and True Love (God).