Hexis derives from echo (to have/hold) and denotes a stable condition acquired through practice. Aristotle used it for virtues — habits that become second nature through repeated action. It appears once in the New Testament: Hebrews 5:14 says 'solid food is for the mature, for those who have their faculties trained by practice to distinguish good from evil.' The hexis of spiritual maturity is not given automatically — it is developed through exercise.
The theology of hexis is the theology of spiritual formation. Maturity is not an event but a trained condition. Discernment — the ability to distinguish good from evil — is a skill, not a gift that falls from heaven. It requires the 'exercise' (gumnazein — from which we get 'gymnasium') of repeated spiritual practice. This is why the disciplines of Bible reading, prayer, community, fasting, and service are not optional accessories. They are the training regimen by which the believer develops the hexis — the stable, trained capacity — to follow Christ in every situation.