The belief system that most people adopt today, either deliberately or more often just through absorbing the general assumptions about life, is humanism, the moral philosophy of which is encapsulated in the golden rule of do as you would be done by. This drives our current obsession with egalitarianism. It even underlies the panicked measures taken to contain Covid-19. But beneath its attractive looking exterior, humanism is an incoherent belief system and little more than a dressed-up version of nihilism.
The humanist does not believe in God* but he does believe in this abstraction of 'humanity'. Setting aside whether there is such a thing as humanity or whether there are just human beings, I would point out that humanity without a divine maker who has given it its own spiritual life and freedom is nothing more than an assemblage of atoms driven by mechanical forces. To talk of love or goodness in these terms is ludicrous. You are not real and neither am I. There is no centre to your being and you cannot in any meaningful way actually matter. You are nothing. Human beings only have any kind of integrity to their being if they have spiritual integrity. Without God we are empty vessels with no authentic individuality.
What humanism does is borrow or steal ideas which can only have any substance in a spiritual universe and apply them to itself. This cannot work because what gives these ideas reality in the first place is being denied. It is like trying to climb while denying the fact of height. Individuality, freedom, love have no meaning in a purely material universe and to pretend otherwise is blatant self-deception.
This matters. You cannot say that as long as we accept individuality, freedom and love, it doesn't matter if we don't acknowledge where they come from. If you don't acknowledge their source you put yourself at opposition with the things themselves which become shadows of their true selves. You are living in a world of fakes and make-believe. You are an imposter, a thief. If individuality, freedom and love only exist because of God then to construct a world and a philosophy and a mode of being that denies God but tries to retain these things is to live a lie. A denier of God has no reason to care for anything because there is nothing except him and he isn't real in any meaningful sense not to mention the fact that he won't last long in any sense at all.
When it comes down to it, the humanist replaces God with self so that self eventually becomes God. This is why today a man can become a woman or thinks he can. I make my own reality. I am God. There is no absolute truth. I can be what I want to be.
When the real Christ is abandoned a false Christ arises, in the realm of ideas at first but maybe eventually in reality. This false Christ will be a humanitarian or, at least, he will appear as one. But his humanitarianism will be an end in itself not part of an over-riding approach to God. He may talk of God but his God will have to fit into the general materialistic attitude with our life in this world seen as primary. He will talk of progress, improvement, development but all these things relate to making the same thing better or apparently better. The spiritual path is not about improvement but transcendence. It does not look to make better men but new men who may be formed from the old men but are more properly described as transformed. Humanism keeps us in profound spiritual darkness because it can never liberate us from the merely human.
* Some in the modern world do believe in God or think they do but their approach to the spiritual is conditioned by the worldly, the complete reverse of which should be the case. That is why I say they think they believe in God. The general trend of their thought shows they don't really. Judge them by their fruits.