Mother Theresa was a nun, and she was very devoted to God. Mother Theresa made a vow to unquestionably obey God when she was 32 years old.
With the permission of her confessor, the Jesuit priest Celeste Van Exem, Mother Teresa made a private vow in April, 1942 … binding herself under pain of mortal sin never to refuse God anything, no matter what He asked of her. (enotes)
I would say this was a vital experience for her, because from that point on she dedicated her life to service for others. She went in some of the most difficult parts of the world and helped people who were in the most desperate need.