Besides her autobiography, St Therese wrote quite a few letters. One that she wrote shortly before she made her first vows is so interesting. She is speaking of how she wants to go to the "mountain of love" -- the heights of love of God, the ascent of Mt Carmel that John of the Cross wrote about.
She told Jesus that she didn't care by what route he would bring her there, as long as she got to the top. Then she speaks of something so amazing. She says that Jesus made her understand that he would bring her there by a subterranean route--a way under the earth, to sort of mine the earth and then go up by a straight route.
But--it was a dark route. And that was exactly how Jesus led her, by the way of spiritual darkness in the night of faith. For more than a year before her death, Therese was plunged into absolute spiritual darkness--not only did she have no consolations, she experienced what can only be called a crucifixion of faith. She was tempted to the darkest places of atheism. She said that during that time, she made more acts of faith than in her whole previous life.
And she endured it all for unbelievers. She willingly suffered this trial of darkness so that those who were in spiritual darkness could find the light.