Christ was crucified at Golgotha - the place of the skull, the mind. So often the mind is Satan's battlefield of choice. Satan's strategy is revealed and the battle lines have been drawn.
Depression is such a mental, emotional and spiritual battle. It is a battle of the mind, but we have already won. We have victory because the work of Christ has been done at Golgotha. Satan's lies are crucified. We live with the power of the resurrection and the mind of Christ.