From whence comes evil?

St. John Chrysostom teaches us that all evil comes first from ourselves and only secondly from the devil.  If we keep our minds vigilant and our hearts strong in the Faith, the devil has no access to us.  The devil only acts on our own evil thoughts and wishes.  When we are angry or envious, or when we have violent feelings toward someone, often or over a long period, we ourselves open the window of our heart to the demons.  Then they feed our sins and nurture them, and we cannot get rid of them easily.  Sometimes we wallow in certain sin for such a long time that it become second nature to us. In the case only God can save us, both from our own selves and from the claws of the demons.