Elizabeth Barrett Browning opens this sonnet with an allusion (reference) to Ephesians 3:18 in the New Testament, in which the apostle Paul discusses God's love and says he hopes the Ephesians

May be able to comprehend with all saints what is the breadth, and length, and depth, and height [of God's love]. And to know the love of Christ, which passeth knowledge, that ye might be filled with all the fulness of God.

Browning, addressing her lover directly, writes,

How do I love thee?

Let me count the ways.

I love thee to the depth and breadth and height

My soul can reach . . .

By using familiar words from a Bible verse, Browning likens her love for her earthly lover to God's love for humankind. Hers is therefore an immense love that encompasses the spiritual, as the words "my soul" indicate. It is deeper and more ideal than she can perceive or articulate.

Browning continues by saying she loves her lover every day, both quietly, like a softly glowing candle, and more strongly, like the sun. She loves him freely and purely. She says she has transferred to him the passion her heart once poured on her childhood griefs and religious faith. She has moved the fervent love she once felt for "saints"—and feared she'd lost—to her beloved. She loves the beloved with all her emotions. She ends the poem by saying that if she should die, she would love her beloved even "better" after death.

Browning's idea of human love is connected to the love of God. It is pure, whole, and fervent. It holds nothing back and is ever present, both bright and steady. It is an idealized and transcendent love.

Sonnet 43 is one of the "Sonnets from the Portuguese" that Elizabeth Barrett Browning wrote to Robert Browning before their marriage, which she presented to him on their honeymoon. In Sonnet 43, Elizabeth Barrett Browning describes her love for Robert Browning as being passionate, virtuous, pervasive, and trusting.

When she speaks of the "depth and breadth and height my soul can reach," she describes the fervency of emotion that characterizes her love. Referring to the "passion put to use in my old griefs," she declares that as deeply as she felt the losses of her loved ones who died, she now feels love for Robert just as deeply. This is a poignant thought indeed, for Elizabeth experienced the death not only of her mother, but also of her brother by drowning. It was after her brother's drowning that Elizabeth became an invalid and a recluse; it was her relationship with Robert that restored her health and inspired her to leave her father's home for good. So, passionate love for Robert replaced her passionate grief.

As Browning describes love in this sonnet, it is virtuous, reflecting both the freedom to fight for what is right and the purity of humility. 

Her love pervades every corner of her existence. During both day and night--"sun and candle-light"--her love is active. It is in the littlest things that occupy her days: "every day's most quiet need." It fills the good times, the bad times, and the in-between times: "breath, smiles, tears." She expects that it will even continue into eternity, if God allows it to.

Finally, she compares her love to religious faith, implying that it has an element of deep trust. The same way she was dedicated to her Christian faith as a child, believing in it fully, so she now fully trusts herself to Robert. And though she may have given up her faith in some "lost saints," she is now able to direct that trusting love toward Robert. 

In this beautiful sonnet, Elizabeth Barrett Browning describes love as fervent, honorable, all-encompassing, and confident.

 Elizabeth Barrett Browning uses "Sonnet 43" to convey the depth of her passion for her beloved. For Browning, love is not merely a word, but an experience that has to be savored. 

In her "Sonnet 43," Browning employs figurative language to compare the strength and quality of her feelings for her beloved.  According to Browning, the act of love should be free, which she compares to patriots who fight for a cause in which they believe.  Love also should be carried out "purely," which Browning insists must be humble and without seeking praise.  Love should include a "passion" which is not diluted by "old griefs," but instead is strengthened by her "childhood's faith."