The term spiritual formation comes from Galations 4:19. The word formed comes from morphe, which means “to shape.” When combined with the Greek prepositions, it is translated as “conformed” in Romams 8:29 and “transformed” in 12:2.
Spiritual formation describes the sanctification or transformation of disciples. The term has become popular for those who want to avoid the baggage that discipleship has carried in recent years. Disciple does seem to dominate the Gospels, while spiritual formation describes spirituality in the Epistles.
Because discipleship has stood the test of time and links believers directly to Jesus, it is the word I choose to use.