God is Dead!
Let's think of any common problem that mankind has faced and excelled over the ages. For example, carrying heavy goods from one place to another. Our ancestors were forced with this problem and had to come up with some effective solutions to solve it. The solutions were dependent upon the geographical and economic conditions of that time. In the earlier days, they might have used some brute force like animals to carry their goods from one place to another. But as time passed by, they started using carts and other means of transportation which were more efficient and less laborious. This is just one example of how the human race has solved a common universal problem over the years. We have come up with newer and better solutions as our understanding of the world around us has increased.
Similarly, there is another universal problem which was addressed by Nietzsche, the existential problem! To find the meaning of life, to find if life has any meaning, and to explore our role as a part of this universe are some examples of this common universal problem. Nietzsche says that different religions all over the world from ancient times have been clever human inventions to solve this age-old universal question of existentialism.
Human beings are social animals and tribal creatures. They tend to attach themselves to a certain group, the meaning of life is to abide by the principles and rules of this group and to demote the motives of other rival groups. It gives a great sense of identity and oneness from believing in any such group and it kind of fills the void of our existentialism crisis. In short, religion has been giving human beings the tribes to live in to get a convenient vice grip on the truth. Religion personalised the world, it gave people purpose and that they were a part of a larger plan. A lot of wars have indeed been fought in the name of religion and in the name of all the fairy tales that we believe in but religion has somehow been a moderate influence on the violence throughout history because it allowed people to organise into massive groups of millions instead of millions of small groups which would have been a disaster.
But the world now has come a long way after the scientific revolution in the last century. Religion has just been a shadow of its former self. No longer the human being today thinks and visualises like our ancestors. Science and technology have given us the power of reason and understanding that we apply to everything around us. It has become impossible to simultaneously be a person who is both reasonable and thinks that someone in the sky is going to punish us for our crimes or that the almighty will heal us with his divine powers. So it has become impossible to use the age-old clever human invention of religion to solve our existential questions. An urge to find a new meaning in life and a way to fill this void has been created by the loss of religion in our lives. An urge to enter new tribes and new groups to fill our void has been created since the religion has lost its true influence.
To Nietzsche, 90% of the people are a mob. He compares them to a camel, beasts of burden, all of their beliefs and values are not theirs but loaded by other people on their back. They are scared people and will never explore the questions of existentialism. They will just blindly follow the herd based on convenience. They will fill their void in other ways.
When he says "God is dead, he remains dead and we have killed him", he is saying it in a very fearful and regretful tone. Neither does he means it literally. He is talking about the death of humanity's pursuit of ethical and moral obligations and beliefs. He is talking about the death of 90% of the people who will fill their void which craves meaning with ready-made answers. Out when religion and in came capitalism, nationalism, socialism, marxism and so many other ideologies. In his book, "The will to power", he predicted that tens and millions of people are going to die in the next hundreds of years. People have started identifying themselves as members of groups first rather than the individual identity. They have started justifying their horrible actions in the name of the group's motives.
Make no mistake, Nietzsche never intended by his statement that one should go back to religion to fill their voids. First of all, because of the scientific revolution in the 19th century, it won't be possible for religion to rule the mob again, but more important Nietzsche wants us to not be the camels. An integral part of being a human being is feeling like we are members of some group that is fighting for good. And if we are not self-aware and honest people we can easily be a soldier for this group. We will always have this fake feeling of doing good for the group and morally justifying all the actions while we do them. We can't and we shouldn't forget about our individuality.