How is sexuality a theme throughout these letters?

Letters to a Young Poet consists of ten letters written by the poet, Rainer Maria Rilke, to an aspiring writer, Franz Xaver Kappus.

Although Rilke advises Kappus on matters pertaining to life and to the true authorial voice, the theme of sexuality is both a latent and driving force behind every piece of valuable counsel in the letters.

You have characterized him quite well with the phrase: "living and writing in heat." And in fact the artist's experience lies so unbelievably close to the sexual, to its pain and its pleasure, that the two phenomena are really just different forms of one and the same longing and bliss... His poetic power is great and as strong as a primal instinct; it has its own relentless rhythms in itself and explodes from him like a volcano. (from the Third Letter).

Throughout the letters, Rilke tells Kappus not to be so anxious to write well that he forgets to experience life and to be open to new influences and lessons which will enrich his writing.

I would like to beg you, dear Sir, as well as I can, to have patience with everything unresolved in your heart and to try to love the questions themselves as if they were locked rooms or books written in a very foreign language. Don't search for the answers, which could not be given to you now, because you would not be able to live them... Sex is difficult; yes. But those tasks that have been entrusted to us are difficult; almost everything serious is difficult; and everything is serious. (from the Fourth Letter).

In Rilke's words, good sex takes effort and 'relentless rhythms' to achieve that frenzy of agonizing pleasure that is savored at the apex of desire. Likewise, good writing involves a similar struggle. In fact, Rilke hypothesizes that anything worthy of achievement in life involves patient, formidable struggle:

Most people have (with the help of conventions) turned their solutions toward what is easy and toward the easiest side of the easy; but it is clear that we must trust in what is difficult; everything alive trusts in it, everything, in Nature grows and defends itself any way it can and is spontaneously itself, tries to be itself at all costs and against all opposition. It is also good to love: because love is difficult... (from the Seventh Letter).

Furthermore, in order to prepare to love, one must learn how to love. This, in itself, is often a solitary process of self-examination and contemplation before one can consider 'merging, surrendering, and uniting with another person.' Likewise, every good piece of writing involves a quiet seeking of the self; it is this silent virtue of achieving personal equilibrium which births written works of the greatest beauty and emotion.

...your solitude will expand and become a place where you can live in the twilight, where the noise of other people passes by, far in the distance. And if out of , this turning within, out of this immersion in your own world, poems come, then you will not think of asking anyone whether they are good or not. (from the First Letter).

So, you can see that the theme of sexuality recapitulates the personal struggles of every good writer who eventually produces works of the greatest clarity and beauty.