A friend recently emailed me this question, and here's my response,
Based on my doctoral studies on discipleship, I'd say that Spiritual Growth is about how well you image Christ. We were made to be image bearers of God, the image got cracked, now Christ (by his Spirit) helps us become more like him the perfect image of God.
What are the key areas of this image in our culture?
a) how do we use our power? Do we use it to serve and protect? Are we making disciples with our power? Are we spreading God's loving rule with our power?
b) do we depend on the Spirit's power or our own strength?
a) how do we respond to authority in our lives?
b) how do we use our authority?
a) Do we evaluate situations based on faith and God's word?
b) are we making fear-based (and flesh-based) assessments?
a) Are we using our voice to speak the truth in love? Are we passing on God's words to others?
b) Are we using our voice to put others down, and big ourselves up?
a) Do we have grace-based relationships with people?
b) Do we use our network of relationships for discipleship?
a) Are we enjoying life as God intended us to?
b) Are we enjoying forbidden fruit?
Based on the above points, are we representing God well?
This is why I take people (including my own family) through the Urban Catechism parts 1 - 3 and then the Image Bearers course, its all designed to gradually help us become more like Christ.