Kierkegaard, the de facto father of existentialism, is worth reading and considering. Warning: Kierkegaard is relentless; he makes a simple statement along the lines of “Christianity is either true or it isn’t. The consequences of either are foundation shaking”. Meaning he will not suffer a comfortable Christian, one who does not realize the salvation of their soul is on the line. Either we do not believe there is a God, and thus there is no objective truth in this world, meaning there is no foundation for moral living; or there is a God, and our strongest desire should be to constantly work out our salvation with “fear and trembling”. I like Kierkegaard, because people like him are a needed shock to our beliefs. We need to test ourselves. We need to truly work out our salvation with fear and trembling. We cannot slump through the day, chasing our empty desires (Aesthetic stage) or replace God with a system of law and ethics like the Jews did (Ethics stage), but we need to sit down in front of a mirror, look into the void, and make a giant leap of faith to live a truly authentic Christian life. Existentialists in general are useful for encouraging the “Authentic life”.
But then you had existentialists like Nietzsche, who was consumed by the desire to detach himself from the fatalistic philosophy of his age. He thought the best way of answering the question of “Why even bother thinking?” was to not answer it at all, but to use the force and domination of your will to live life. Kierkegaard brought a reader from that fatalism to authentic faith. Nietzsche brought a reader from fatalism to egoism and a pyschotic detachment from society. Nietzsche may be one of the most overrated thinkers in history. His philosophy is riddled with holes, and it only appeals to the egoist who thinks he can determine his own truth in all matters. A typical elitists philosophy that claims only a few people can become such a man “superman” and Nietzsche even claimed that he understood the true Jesus more than any religion (he appreciated Jesus but disliked his altruism). And he claims that Christianity was a hoax religion thought up as a means of revenge against the Roman Empire. Nietzsche eventually went insane, a natural end of his philosophy.