"No man is an island,
Entire of itself,
Every man is a piece of the continent,
A part of the main."
Thomas Merton used "No Man is an Island" for a title of his book.
As much as we'd like to think that we can be wholly independent and free from dependence on anything consider the fact that your very life depends on other things whether you like it or not.
You are dependent on the billions of tiny microorganisms that are in your body and on your body. If I could remove them all from your body you would surely die. Your body wouldn't be able to digest and break down the nutrients you need without this symbiotic relationship. You would be subject to manifold infections being devoid of the barrier of good organisms that populate your body. You would wither away and shrivel into nothingness before your certain death.
The same thing happens to your spirit if you remove God from your spiritual body. You slowly wither away, devoid of the nutrients you need for a spiritual life and you die a spiritual death. We depend on God to nurture us and give us our spiritual health.
Perhaps you make the claim to "spiritual but not religious". If you do you have been sold a bill of goods. I've been there. How wonderful to think that we are so independent that we can survive such a farce, such an empty thing - how cocky, immature and completely wrong! It's not the mature spirit that believes that he or she does not depend on anybody else but themselves, it's a immature spirit. It's the same attitude that makes a teenager believe that they can take on the world, leave their home, free themselves from the tyranny of oppression of their parents. Most children grow out of that stage and realize how wrong they were.
This raises the question of whether you can be a Christian and not go to church.
Certainly you can be a Christian and not go to church.
You just can't be a very good one.
The Body of Christ nurtures us and prepares us to go out into the world and do His will. Paul talks about us being members (actual pieces like a hand, a foot, a heart) of the Body of Christ -- so what good is a hand or an ear all by itself? What can a head do without a body? What good is your arm without a shoulder connected to a torso? What are any of these without the rest of the parts of the body?
They are ineffectual.