I've found this to be a helpful one to which I've returned again and again as I seek to grow in the Christian life: deal with sin, mature in righteousness, etc.
I can't remember which book I first saw this in.
"This life, therefore, is not righteousness but growth in righteousness, not health but healing, not being but becoming, not rest but exercise. We are not yet what we shall be, but we are growing toward it. The process is not yet finished, but it is going on. This is not the end, but it is the road."