In the woods of New Hampshire, near the beautiful Kancamagus River, I once had a picnic with some friends. We were talking about the transforming power of the word of God on the mind. I dug out a small rock from the forest floor and took it to the river, where I fished out another rock of similar size. I asked them to look at the two rocks and compare them. Someone said, “One of the rocks is covered with dirt, but the other one is clean.” So I crouched down and swished the dirty rock in the river for ten seconds of so. It came out wet and clean of all dirt. Again, I asked them to compare the two rocks. They took them and looked at them carefully. Another of the guys said, “The river rock is smooth and shiny, but the forest rock has all kinds of sharp edges.” New Hampshire is the Granite State, and this rock had crystalline peaks all over, hard as granite. I asked, “How do we transform the forest rock into a river rock?” The answer was simple: put it in the river. But for how long? Well, perhaps a century or so! A hundred years of river water gently flowing over the surface of the forest rock, carrying small granules of sand as a mild abrasive, would transform that jagged rock, and make it as smooth and shiny as the other. The patient activity of the Kancamagus River would do the work.
So it is with the transformation of a Christian from immaturity to maturity. Some dirt particles (sin habits) get washed off immediately after conversion, but the rest of the change is more difficult. Transformation only comes by immersing the mind in the word of God, allowing it to wash over our thoughts, until gradually we have learned to think as Christ does. And this is precisely what Paul is commanding us to do in Romans 12:1-2. (Andy Davis in An Infinite Journey)