Perhaps you have seen the incredible collections of petrified wood in some of our National Parks or Monuments, or maybe you have seen individual examples in any number of other places. A geology site briefly explains how material becomes petrified: Petrified wood is a fossil. It forms when plant material is buried by sediment and protected from decay by oxygen and organisms. Then, groundwater rich in dissolved solids flows through the sediment replacing the original plant material with silica, calcite, pyrite or another inorganic material such as opal. The result is a fossil of the original woody material that often exhibits preserved details of the bark, wood and cellular structures (geology.com/stories/13/petrified-wood).
There are a few interesting aspects to this process-the burial, the protection, the replacement and the resulting appearance. Twice in the gospel of Mark, the writer uses a term to describe the condition of the disciples' hearts as hardened. Immediately after Jesus feeds the 5,000+, He tells them to get into a boat. When Jesus came walking on the water, Mark writes that they were troubled and fearful, amazed and marveling "for they had not gained any insight from the incident of the loaves, but their heart was hardened" (52). Ironically, the second incident happened in a boat following Jesus feeding thousands of people, again. They misunderstand Jesus' warning about the leaven of the religious leaders, and Jesus laments, "Is your heart still hardened?" (8:17).
BDAG defines the word we translate “hardened” (πωρόω) in this way: "To cause someone to have difficulty in understanding or comprehending, harden, petrify, make dull, obtuse, blind, close the mind" (900). The truth was buried from their understanding, their preexisting, preset points of view blocking its penetration, and the result was their missing the important point. The truth could not get through to their petrified hearts.
Why do we fail to understand basic, vital Bible truths, like the essential nature of baptism, the abrogation of the Law of Moses (including the Ten Commandments), the emotionally difficult teaching of Jesus about marriage, divorce, and remarriage in Matthew 19, God's law regarding sexual purity, and the like? Why do we struggle with worry, fear and doubt? Why do we lack the courage to boldly share Jesus with the lost? Often, the answer to each of these and similar questions is the same as why the disciples feared and faltered.
We should pray for our hearts to stay soft, receptive and moldable to Jesus. We cannot let our ignorance, resistance or outside influences harden our hearts. In fact, that very prospect should make us, well, petrified!