There are many spirits, but only one Holy Spirit

Human beings are spiritual by nature, our spirit lives within us.

I find artists, for example, very spiritual, and I suppose it is 
because they express themselves from inside out.
Children are very spiritual, and very in their nature, too!

If you are "spiritual but not religious", then you probably have a 
particular aim, or several; maybe to be happy, feel "connected", 
centered, grounded, loving, present, energetic....... etc.

With the Catholic doctrine it is about obedience. 
Obedience is a word that is enough to make people flee, 
to send shivers down the spine.  

One might ask: "what is in it for me", "why would I agree to rules 
that does not make sense, and agree to do things that are boring 
and that I do not understand?"

And again: "what do I get out of it?" 

And then, amongst Christians there are those that are "trying hard" 
to come close to God.
They can never succeed, as it is their "trying hard" that blocks God.

It is God that does everything. That does not mean that we do nothing.
So what is required of us?

Obedience. Prayer, Mass, Bible readings.

That our attitude is one of trust, trust in what we cannot see; 
acts of faith.
It is not us that are in charge, we are being led by God. 

It is a constant work of self emptying; we have to "get out of the way" 
in order that God can fill us.

And we need to have the desire. Deep desire. 

The desire that never goes away after we have seen and experienced
something that is "not of this world", but that is more real than anything
in this world.