Can only abstract objects exist by necessity Part1

Prof. Liebegott in a wonderful comment on my previous post argued that theists are fundamentally mistaken in their belief that God could be a necessary being.  

The problem here is that there is a serious category mistake.  That is, the claim is incoherent because God is not the kind of thing that could be a necessary being.  Other examples of category mistakes are claims like the number two is blue or my dream weighs 64 pounds numbers are not the types of things that have color and dreams do not have weight.  So these claims are false because they attribute to an entity a kind of property that it could not in principle have.

Prof. Liebegott, following our former teacher Paul Draper (Purdue), argues that only abstract objects can be necessary, not concrete objects.  

Concrete objects are the kinds of things that we are all familiar with tables, chairs, people, etc.  But what are abstract objects?  Many examples could be given.  I will focus on two:  mathematical truths and propositions.  It seems as though 1+1=2 even if no one had ever considered the claim.  It seems as though it was true long before any conscious mind (save God if God exists) had any thoughts.  Abstract objects help us to account for this intuition.  We suppose that there were abstract objects (which are the mathematical truths or maybe that which make the mathematical claims true) before any concrete objects existed.  That is, math was true before there were trees (or any other concrete objects.)  A second example of an abstract object is a proposition.  Propositions are different from sentences.  A sentences is a collection of sounds in a particular language.  A proposition is what is expressed by that sentence.  We can express the same proposition in many different languages.  How is this possible?  Well, perhaps propositions are real things that we somehow access.  All of us can access these propositions and then express them with different linguistic markers.

Abstract objects are weird entities and it is hard to say exactly what they are like.  But there is pretty good evidence that we do need some kind of entity to play these roles.