What three reasons does the editor give for Harriet Jacobs ability to write so well?

From the text:

It will naturally excite surprise that a woman reared in Slavery should beable to write so well. But circumstances will explain this. In the first place, nature endowed her with quick perceptions. Secondly, the mistress,with whom she lived till she was twelve years old, was a kind, considerate friend, who taught her to read and spell. Thirdly, she was placed in favorable circumstances after she came to the North; having frequent intercourse with intelligent persons, who felt a friendly interest in her welfare, and were disposed to give her opportunities for self-improvement.