The desert fathers, because of their clairvoyance, have seen more clearly the approach and assault of spiritual forces against a Christian who wishes to pray, and have written about the development of sin from within a person.

The first stage is the intrusive thought, which “pops into our head” – a mere suggestion of doing something. This is not a sin, but if within us there is some part of the heart that is not cleansed, then the suggestion will take root and turn into a temptation. The person then begins to contend with the temptation – weighing up the pros and cons of the suggestion. This is also not a sin, because the temptation can be rejected in the mind, but this is already a dangerous place to be in. Without being rejected the temptation becomes a desire, and the person will find a way to carry out the evil deed suggested. This is a sin which must be repented of – it is committing the sin in thought – although even here there is the possibility that the person will not – in the end – carry out the deed. The next stage is to commit the sin in deed as well as thought. If this sin is not repented of then it may completely “possess” the person and become habitual, like a second nature.