If hydrogen and helium are the most abundant elements in the unoverse, then why are living organisms composed primarily of carbon, oxygen, nitrogen and also hydrogen?

Most of materia isnt life.

Explanation:

The living organisms (life) aren't the most abundant thing in universe.

Hydrogen and helium are present in everywhere, but life isn't.

There is no reason to think because we have a lot of a thing, the life must be made for this thing.

The organic life just can exists because some mysterious properties about carbon, that is the basic foundation of life, carbon is a special element, why? We don't know, actually, it's a huge problem for science discover why the carbon can makes life be possible and other elements can't. But we know is this element that makes life possible.

So, note there isn't relation about the quantity of a material in Universe and the life constituition. In addition, look around, organic materials are very rare in Universe, Earth is one in lots of places and in most of this places there isn't sign of life.

Even in Earth the life looks abundant, in Universe it isn't, the same way in Universe the Hydrogen and Helium are abudant, in Earth isn't soo.