The world is not what we perceive. (Through the five senses) These are devices to awaken us to the world. The world is what we know it to be through direct knowledge, noesis, intuition. So Merleau-Ponty was not quite right. Neither is the world a (17th century) machine. It is a mind, or, rather, a soul. Your atheist, but not so much your agnostic - he might be considered to be a sceptic - is stuck in the 17th century mind set of Newtonian physics of the mechanistic universe.
The false dichotomies of the mechanistic world view are a product of the reasoning mind. We have learned that matter is to be contrasted with non matter. A more subtle view is that matter is that which is superimposed by form. Matter is a kind of universality - its more or less evenly distributed throughout space while form confers individuality on matter. The many confer individuality on the one while the one confers universality on the many. Universality is closely associated with intuition and through intuition to faith and understanding. Form is closely associated with reason and through reason to knowledge. We seek to define the universal in terms of the form, specifically, our own form. It was Heraclitus that said man is the measure of all things. This is a bug not a feature.
The world is not what we perceive. Neither is the truth what we make of it. But this doesn't mean there is no objective truth. The world is grounded in reality. Its just that the truth, in itself, is unknowable. Only in its particulars is it continuously and endlessly revealed while never being exhausted. The proliferation of red roses never uses up all the red. This is why knowledge always fails. You can't own the truth. Red roses participate with redness but don't use it all up. This also serves to explain why every moment of mind is a reiteration of self, soul. And in turn it follows that it is not true there is no abiding soul as the Buddha is reported to have claimed. Redness is there for the next iteration of a red rose for infinity.
Confusion about this makes it seem we are free to make our own truth, but really, that we seem to find the truth we look for is something of an illusion. There are boundaries. Moral truth is real. Its just that it can't be exhausted - like the red of the rose. Its not a thing in itself, and neither is God. We find God through faith. That is also how we find moral truth. You can say that reality is what we think it is but that is an error. It is measuring the universal in terms of the particular. And, another thing to consider about a moral compass is not so much that you can see where you are going but rather you know where you are coming from.
God confers on man universality. Man confers on God, individuality. Put another way, God confers on man eternality, everlasting life. Man confers on God temporality. The sun, the planets follow this same scheme writ large.
To summarize, its not about finding the one true answer to life's profoundest questions. They simply are not there. Rather focus on the search for the answer, the ultimate truth. As Kierkegaard put it, life is a mystery to live not to discover. You can't own it but, better yet, you are permitted to endlessly seek it out. Its much easier to drink from a pool with cupped rather than grasping hands. And, honor, duty, courage, devotion, love, truth, wisdom, understanding, faith, beauty, and liberty are to sentient life forms everywhere what red is to the rose.
The moon is high in the night sky, almost full. But the silence of this night outshines her lovely face. Contemplate "nothing said can do more for enlightenment than what a finger pointing at the moon can do for seeing the moon."