"Spiritual formation in the tradition of Jesus Christ is the process of transformation of the inmost dimension of the human being, the heart, which is the same as the spirit or will. It is being formed (really, transformed) in such a way that its natural expression comes to be the deeds of Christ done in the power of Christ.
The progression of spiritual formation is outlined in various passages of the New Testament. It is most fully spelled out in II Peter 1: “Now since you have become partakers of the divine nature,” the writer says, “applying all diligence, in your faith supply moral excellence, and in your moral excellence, knowledge; and in your knowledge, self-control, and in your self-control, perseverance, and in your perseverance, godliness; and in your godliness, brotherly kindness, and in your brotherly kindness, love.”