I teach a course in human development across the lifespan at a local university. In my first lecture I asked the class: "If we were to draw a picture of the course of human development, what would that picture be?" Some suggested a strait line, like a timeline, with a beginning, middle and end. Others said the course of a human life is like a bell curve, starting low, reaching a pinnacle and then going in a steep decline. Someone suggested a circle, another a spiral upward. One pictured life as a flower, starting as a seed, growing to full flower and then dying. One envisioned the human as a lump of clay with two or three hammers pounding it into shape.
What these pictures reveal are two essential elements of the shape of human development. 1) It is directional, that is, humans grow and change through time. 2) it is bi-directional or interactive, that is, biological, psychological and social forces shape human development through time, even as the individual has influence on these forces.
What is interesting about human development and what makes the study of it so complex are these elements of change and interaction. Just as the individual is influenced by the social context in which a person develops, so can the individual influence that social environment so that two people growing up in the same social environment would not develop the same. In a similar fashion, eating junk food will change our biology, which will in turn influence our development. In this way all of life is determined by the interaction of individuals with the biological, psychological and social forces in their lives.
Teaching this course at a secular university, I did not feel free to introduce what I consider another force in human development: God. We often think of God as immutable and unchanging, but if we take human development as a model for our relationship with God, the truth may be that God changes from our interaction with God just as we are changed. The change in God may not be as great as the change in the individual, just like the change in the social environment that one person affects is not as great as the influence of the social environment on the person, but there is change nonetheless.
The Psalmist attests to the "too wonderful" knowledge that God has made us, searched us, knows where we go, and has numbered our days (Ps. 138:1-18) and states "In your book were written all the days that were formed for me" (v. 16). Could it be that the last chapter of that book is not yet written, because both the author and the subject might change?