It's no secret that I am very interested in spiritual formation. My entire life is invested in changing from my subhumanity into Christlikeness (See Galatians 4:19, e.g.). I'm not there yet, but desire this so much that I spend much time, one-on-one, with God.
One of my guides in this process of change is Henri Nouwen. I did not know Henri personally. Once I wrote him a letter with a question. To my surprise, he responded. Mostly I know Henri through his writings.
Henri writes: "Spiritual formation, I have come to believe, is not about steps or stages on the way to perfection. It’s about the movements from the mind to the heart through prayer in its many forms that reunite us with God, each other, and our truest selves." (Nouwen, Spiritual Formation: Following the Movements of the Spirit, Kindle Locations 152-154. Note: anyone interested in being formed into greater and greater Christlikeness should get this book.)
Spiritual formation happens in the presence of God. You cannot consistently dwell in the presence of God and stay unchanged. On rare occasions there is an instant morphing, a kind of quantum leap into greater Jesus-likeness. But mostly this is a slow-cooker. The word "abide" is not for microwaves.
Spiritual formation is hard to measure quantatively. In fact, it cannot be quantized. Nouwen instructs that "it is of great importance that we leave the world of measurements behind when we speak about the life of the Spirit." (Ib., Kindle Locations 151-152) We live "in a society that overvalues progress, development, and personal achievement, the spiritual life becomes quite easily performance oriented: “On what level am I now, and how do I move to the next one?”" (Ib., Kindle Locations 147-149)
When it comes to spiritual formation, rejection comparing your growth to that of others, and throw away the measuring rod. Nouwen quotes Russian mystic Theophan the Recluse:
"I will remind you of only one thing: one must descend with the mind into the heart, and there stand before the face of the Lord, ever-present, all seeing within you. Prayer takes a firm and steadfast hold, when a small fire begins to burn in the heart. Try not to quench this fire, and it will become established in such a way that the prayer repeats itself: and then you will have within you a small murmuring stream." (Ib., Kindle Locations 155-158)