The Logos of God is like a grain of mustard seed (Matthew 13:31): before cultivation it looks extremely small, but when cultivated in the right way it grows so large that the highest principles of both sensible and intelligible creation come like birds to revive themselves in it. For the principles or inner essences of all things are embraced by the Logos, but the Logos is not embraced by any thing. Hence the Lord has said that he who has faith as a grain of mustard seed can move a mountain by a word of command (Matthew 17:20), that is, he can destroy the devil’s dominion over us and remove it from its foundation.
The grain of mustard seed is the Lord, who by faith is sown spiritually in the hearts of those who accept Him. He who diligently cultivates the seed by practicing the virtues moves the mountain of earth-bound pride and, through the power he has gained, he expels from himself the obdurate habit of sin. In this way he revives in himself the activity of the principles and qualities, or divine powers present in the commandments, as though they were birds.
~St Maximos the Confessor