Reclusion and ascetic discipline
After his tonsure, Isaac embraced an exceptionally severe reclusion, shutting himself in a small cell. The accounts of his life stress the rigor of his diet: he is said to have taken only a single prosphora and a little water at the end of each day, while in one recension Saint Anthony passed him a blessed loaf through his cell window every other day.
It was in this extreme solitude, after about seven years, that he met his great trial. The demons came to him in the guise of angels of light, and finally one appeared whom he took for Christ himself; deceived, Isaac worshipped him. The deception broke his health: he was left crippled, unable to walk or speak.