Assuming belief in the supernatural, if humans have a spirit, can it grow?
Christians would answer affirmatively, but maybe the real question is whether its’ development is something that they take an active part in. Physical training is undoubtedly vital for sportsmen and women, who live lives dedicated to getting the best out of their physical bodies and skills. They commit to following a monitored diet and fitness regime. They don’t expect to simply turn up and be able to perform and play to the best of their abilities. Similarly, I believe that if Christians are to take their faith seriously, then the same principle of training and commitment to a certain lifestyle needs to be applied. Whilst Christians are saved by God’s grace, and cannot earn their salvation, they are clearly responsible for their lives and how they live them. St. Paul says that “while physical exercise has some value, spiritual exercise is much more important, for it promises a reward in both this life and the next” (1 Tim 4:8). In my view, the question of what this “spiritual exercise” looks like can best be answered by studying the spiritual disciplines such as solitude and fasting that have long been practiced throughout the ages and that were also central to Jesus Christ’s life – Christ was tempted by the devil whilst in the middle of a long period of fasting and before he was arrested to be crucified, He purposefully spent time alone in prayer.
See: Dallas Willard – ‘The Spirit of the Disciplines’.