Inside my body are 57 years of issues, problems, stresses. These issues, problems, and stresses present themselves at various times, for who knows what reason. Often there is a triggering event to pull the issue up. Some deep, chronic problems might take a long time to surface.
I visualize my unfolding health issues as the layers of an onion. Under each layer is another layer, each one deeper and closer to the core of me.
I also liken this to sin. If the Lord confronted us with the entirely of our sin problem at the moment of salvation, we would be overwhelmed and discouraged. Instead in His wisdom, the Holy Spirit reveals one issue at a time with the express purpose of transforming us into the image of His Son.