It will depend on the state of the cobweb as to the spiritual interpretation. A spiders web can suggest the symbol of the eight pointed star, the mandala - an aid to meditation - and hence the Buddhist eightfold path to spiritual enlightenment. A dirty cobweb, however, denotes that spirituality is contaminated in some fashion. The cobweb, because it is easily damaged, signifies indecision, perhaps an idea that has not quite crystallized yet. On a purely practical level the cobweb symbolizes unused talents and potential which has been allowed to go stale. You might like to consult the entries for Spider and Star in Shapes/Patterns for further clarification.