If done properly, where would Spiritual Formation fit under within systematic theology?
May I ask why you preface the question with "if done properly"? It adds ambiguity to the question. I would expect to find it primarily in theological anthropology with some mentions in bibliology, Christology, ecclesiology, hamartiology, pneumatology and soteriology. This is a good example of why the Orthodox are more holistic and less analytic than the West.
Christian:
If I am not mistaken, some more modern ST have a "christian living" category, I would imagine that is where it would fit.
Read long time ago that christian educator's primary responsibility is to foster Christlikeness in believers, so it would seem that spiritual formation and Christlikeness are interrelated.
Maybe you can check your ST to see what they say about Christlikeness, and what process is recommended to achieve such.
In much of the church it would fall under theosis/deification which falls under gnosiology/epistomology which I find interesting. The Lexham Survey of Theology classifies it as a theory of atonement, a surprising placement. Symeon the New Theologian is a good starting point to understand the gnosiology placement. I'll have to mull the LST choice over a bit longer, but I think I understand the why -- sort of -- a focus on the saved/not saved dichotomy rather than the newborn/mature Christian continuum.
