This is not a question I relish; some years ago, as a newly-minted PhD, I was called for interview for a lectureship in systematic theology. Not unreasonably, the first question, in faux-ignorant terms from the Dean, was ‘So what is systematic theology?’
‘Good question,’ I thought.
‘I don’t have an answer,’ I thought.
‘I’m not going to get this job,’ I thought, as my jaw went up and down with no sound emerging from my mouth…
In a narrower definition, systematic theology is an attempt to present an ordered account of the teachings of the Christian faith, with a particular eye to their coherence and interrelation. The term ‘systematic’ witnesses to this concern for order. Arguably, this narrow version began with Schleiermacher’s The Christian Faith (first published in German in 1821-2; substantially revised 1830-1).
These days ‘systematic theology’ tends to be used for any full account of Christian doctrine, and so the term can encompass early statements that were not especially self-conscious about the structure of the system: Thomas Aquinas’ Summa Theologica, or John Calvin’s Institutes.
Accounts of Christian doctrine tend to the expansive. None of the above mentioned books are small – Schleiermacher is the only one to have a standard English edition in one volume, indeed – and that is a hefty volume. Karl Barth’s Church Dogmatics, weighing in at nearly ten million words, and far from finished, is the modern classic of the genre.
So 140 characters is bucking the trend somewhat.