"To My Dear and Loving Husband" is one giant love fest. And it's not about just any old kind of love. We're talking unconditional, unstoppable, undying love. The speaker spends the bulk of the poem coming up with different ways to describe her love for her totally awesome husband, which is so strong that not even a river can "quench it," she claims. In addition to the speaker's love for her husband, we also learn a little bit about her husband's love for her. By the end of the poem, the speaker suggests that the love between her and her husband is so powerful that it can somehow give them immortality. Now that's love.
Love is a powerful, binding force. In the poem, for example, it has the ability to make two people one.
Love defies definition. The speaker describes it in so many different ways because there is no one, simple way to explain it.