Depression is one of the worst conditions a human being may suffer.
There are several reasons for the occurrence of depression. One that is very common results from feeling that life is meaningless. Combined with the fact that nobody can escape death, some people experience life as very painful. They do not suffer from anything in particular, yet they have convinced themselves that from an existential point of view, their very existence is pointless.
It was the French philosopher, Nobel prize winner Albert Camus (1913-1960), who summed it up in a short observation: there is only one philosophical problem—whether or not one should commit suicide.
What is most remarkable is that most people, including those who do not believe that life has any purpose and consequently are depressed, desire desperately to live, and will fight to maintain and obtain every second to live.
The most notable example is the pauper who lives on the street, surviving on the leftovers of others and the (often small amounts of) charity he obtains from the passersby. He continues to do so, even though he knows that in all probability, he will continue to live as a pauper. He prefers to live this kind of life rather than ending his life. Should he be asked why he does not end his life, he will respond that he hopes that one day his lot will be far improved, yet, even should this not be the case, he still prefers, however difficult, to live the life of a pauper than not live at all.
From a purely rational point of view, this makes little sense. Why not commit suicide? True, the fear of committing suicide plays a role—yet this still does not answer the question as to why many people are prepared to live under the most painful of circumstances for years. Why do they not end it all, within a second, however difficult this may be?
The answer to this mystery is that there is another side to the human being that has nothing to do with rationality or logic. However, this other “side”—the phenomenon of belief, faith and commitment—is just as real as rationality.
Above all, this additional element of a human being is the awareness that there is more to life than its psychical dimension. Love, emotions, loyalty, and hope all play a substantial role in our lives—however, these are all non-rational entities. Nobody can explain precisely, in real terms, why music and art possess beauty.
The important point is that they cannot be explained in purely scientific terms. Science deals with cause and effect, not with purpose and meaning. In fact, rational knowledge negates the meaning of life. Science does not, nor should it, attempt to address the question of the meaning of life. This question lies outside the purview of science and the scientific method. Science does no more than establishing hard facts—hard facts independent of meaning.
Those who claim with pride that they consider only the rational and the scientific, are essentially asserting they deny that they have an emotional life of meaning, love and beauty. This is the sentiment of the foolish, not the wise. Claims like these are unrealistic; they ignore the non-rational side of their lives while making daily use of it.
Such people make crucial decisions in their lives that are completely non-rational! In their work, Nobel laureate psychologist and economist Daniel Kahneman and the late cognitive and mathematical psychologist Amos Tversky demonstrated the prevalence of irrational human economic choices (“Prospect Theory: An Analysis of Decision under Risk,” Economica 47:2 (Mar. 1979), Daniel Kahneman and Amos Tversky).
In modern neurological terms we may say that it is the difference between the left and right hemispheres of our brains. The left brain is analyzing and scientific. It takes things apart to see how they work. The other side, the right hemisphere, is where our faith and emotions reside. It is where we put things together to see their meaning. It is non-rational but just as genuine.
The Book of Kohelet (Ecclesiastes) conveys a message of despair and describes all of life as “hevel,” “vain,” i.e. empty and meaningless—yet, the penultimate verse reverses this message. The author (King Solomon, according to tradition) realizes that he has erred. He writes: “The end of the matter, all having been heard: Fear God, and keep His commandments: for that is the whole duty of man (Kohelet 12:13).” This verse states clearly the duty and purpose of man.
We may not know why the purpose of life is to fear God and keep His commandments, but, subconsciously, we know that Kohelet is telling the truth. We always knew that there is meaning in our lives. However, we do not know this by means of science and rationality, rather, a higher intuition fills our minds and radiates into our reality.
This is the secret of the unique ritual of the Para Aduma, the Red Heifer, which was slaughtered, burned and water containing its ashes was sprinkled on an individual who had come into contact with a corpse—thereby purifying this ta’me (ritually “impure”) individual. In the process of purifying this individual, the kohen (priest) sprinkling the water becomes ta’me! 
The tremendous paradox is clear and apparent—and the entire ritual is completely non-rational as far as our intellect is concerned. However, the intuition we utilize throughout our lives tells us that we can accept this ritual even as the intellectual problem persists. Life includes many paradoxes; our experience of love, emotions, and beauty teaches us that these incorporeal elements are just as true as the concrete facts of scientific knowledge.
It is not for nothing that philosophers have said that “he who confronts the paradoxical exposes himself to reality (Friedrich Dürrenmatt).” And, “Life is a paradox. Every truth has its counterpart which contradicts it; and every philosopher supplies the logic of his own undoing (Elbert Hubbard).”
We need to accept the paradoxical as a fact of life. It is the fluid of all existence. It was Nobel winner, Isaac Bashevis Singer (1902-1991) who seized this paradox by his famous remark saying, that “we must believe in free will, we have no choice.”
Indeed, in the words of Abraham Joshua Heschel:
“The search of reason ends at the shore of the known… reason cannot go beyond the shore and the sense of ineffable is out of place where we measure, where we weigh… We sail because our mind is like a fantastic seashell, and when applying our ear to its lips, we hear a perpetual murmur from the waves beyond the shore.”
 See Chief Rabbi Lord Jonathan Sacks, “The Great Partnership, God Science and the Search for Meaning,” Hodder & Stoughton, London, 2011.
 See Bamidbar 19.
 “Man Is Not Alone: A Philosophy of Religion,” Abraham Joshua Heschel.