Knowledge, which is also her motive for becoming the book thief.
The power of words, as she understands their power and wishes to make that power her own.
A place to feel safe during the turmoil of the war that threatens her each day of her life, which is what the books eventually become for the young girl.
Her weakness that she soon turns into a strength is her ability to read. Liesel uses the power of words and adds it to her own strength, and also to better herself after realizing that her inability to read was hindering her.