Tennyson wrote this poem after the death of his beloved friend Arthur Henry Hallam in 1833. This isn't the whole poem - I abridged it to about half the original size. The full poem is here:
poetry.about.com/od/poemsbytit...
In 1833 there were very few atheists: Darwin's Origin of Species was not published until 1859. The only credible explanation for the wonders of nature was that they were created by God. You could drop tiny seeds into ordinary soil, and in a few weeks they would become flowers with colours that were more intense than anything made by man. This apparent miracle seemed to imply the existence of God. People still look at flowers in spring and experience the same sense of wonder.
Suicide - or self-destruction - is actually pro-survival in an evolutionary sense. Evolution works for the genes, not for the individual. Genes encode survival strategies. Survival of the Fittest implies the destruction of the unfit. Misery is negative-feedback: it signifies that your survival strategies are not working. The lethargy and ineffectuality misery induces would in a primitive environment quickly remove you from the gene pool.
The remedy is not to end your life, but to change the circumstances in which you are living. Your genes might work better in a different environment. There are many people who overcame disadvantages and, like Tennyson, came back from the brink of suicide to become happy and successful. Well, happy or not, he was successful and he lived to be 83. Not many Victorians did that.
We inherit the capacity to learn things. For example, genes can't pass on language but they can pass on the ability to learn a language. Language is one of the great advantages of humanity. The sum of human learning and experience rolls forward like a snowball gathering size and weight.
We also inherit the capacity to believe things. At one time, when mankind lived in small communities, common beliefs created bonds between members of a tribe. People who believed the same things would act together against a common threat. Now that people with different beliefs can communicate more freely, beliefs have become the cause of most of mankind's troubles.
The most obvious Belief Systems are religions and superstitions. It's less obvious that social sciences, such as Psychiatry, Politics, Medicine, are substantially Belief Systems. Whatever is currently believed is held to be true and beneficial - even though it is obvious that past beliefs were wrong and dangerous.
There is a persisting maxim that one should fight for one's beliefs. A better maxim would be that one should purge oneself of all beliefs.