Thinking clearly about the word 'they'

Is there such a thing as a singular 'they' in the English language? That is, can the word 'they' (also 'them' and 'their') be used to refer to one person, or is it only appropriate for two or more people? Consider this sentence:

Somebody left their dog tied to this telephone pole.

This sentence sounds perfectly natural and reflects the way native speakers use the language. The reason 'their' sounds appropriate for a 'somebody' who is only one person is because we don't know the gender of this somebody. We could say 'his dog', defaulting to the masculine, and that might please some grammar nazis, but it would sound less natural to most English speakers.

But how about this sentence?

Abraham Lincoln liked to read books when they were a child.

Some of us are going to have to read that one twice because when the word 'they' pops up we immediately imagine that there are some other people alongside Abraham Lincoln that are being referred to. There isn't anybody else, and so this is another sentence using 'they' to refer to a single person, but in a way that is jarring and confusing for native speakers. What makes this sentence different is that when the subject was 'somebody' the gender of the subject was ambiguous, but when the subject is Abraham Lincoln we fully expect the use of the masculine pronouns, 'he', 'him' and 'his'.

This second awkward use of the word 'they' to refer to a single person is not the natural evolution of a living language, but a ham-handed political effort to deny God's design for humankind as male and female. It is one aspect of our current revolt against God's created order, and as such it must be opposed by Christians who are called to speak the truth in love.

A special case of this second nefarious use of 'they' for a single person is using 'they' to refer to God. Of course God isn't male in the same way that Abraham Lincoln is, so the revisionists might seem to be on firmer ground here. Why not use a gender-neutral pronoun since God is neither male nor female? The problem with this line of thought is that it elevates human reason over God's revelation of himself. It was God who inspired the Biblical authors to use masculine pronouns to refer to him as well as the terms 'Father' and 'Son'. Unless we think we're wiser than the God who revealed himself in this way, we must follow his example and reject the word 'they' as an acceptable pronoun for God.