Katherine Patterson's novel, Jacob Have I Loved, has several values, virtues or morals which are important in the novel.  The most important moral is that love can truly be the value which enhances life and relationships.  Louise and Caroline are twins with the story being narrated by Louise.  Because of her narrative looking back at her life on Rass Island later in her life, everything is seen through her eyes.  She looks at her terrible jealousy of her twin, Caroline, who seems to have everything, beauty, musical talent, and the love of everyone around her.  Louise, in looking back, sees her hatred and envy of her sister as comparable to her grandmother's bitter influence on her and her family which illustrates the value that envy and hatred could turn her into a bitter woman without joy or love in her life.  Louise  learns that the Captain considers her strong in every way except that she is beginning to act like her bitter grandmother.  The moral for Louise is that she has strengths also, and does not need to envy her sister Caroline.  When Louise remembers her parents telling her that they would miss her more than Caroline, she understands that she is loved and has the courage to follow her dream which illustrates that love is liberating and doesn't need to be forced.  When she leaves the island for the mountains and midwifery, she illustrates the virtue of giving back or helping those who need her skills.  When she delivers twins where one is more delicate than the other, she finally understands her own twin, Caroline, and her useless envy of a sister she now knows she loves.  Her value of her sister shows her own maturity, that she now understands what true love is with no need for her to hate or envy her sister.