In this sonnet, the speaker states that because of being enveloped in the love of her beloved which comes from God, the world can do her no harm. In the last part of the sonnet, the speaker says that the love she and her beloved share is watered, rooted in, and protected by heaven. Their love can't be touched by mankind—the wealth it offers is given by God, and only God can, therefore, make them poor by taking it away. Their love is spiritual and from God, and thus safe from worldly harm.
A metaphor is a comparison not using the words "like" or "as". Browning compares love to a hand, soft and warm. She compares the way people might try to hurt them to a "stab." She compares their lives to lilies.
Alliteration occurs when the same consonant is used at the beginning of words in close proximity. "Sharpness" and "shut" are alliterative, as are "lilies" and "lives," along with "wordlings," "weak," and "whitely."