The Virtue that Requires the Greatest Effort

“The brethren also asked [Abba Agathon], ‘Amongst all good works, which is the virtue that requires the greatest effort?’ He answered, ‘Forgive me, but I think there is no labour greater than that of prayer to God. For every time a man wants to pray, his enemies, the demons, want to prevent him. For they know that it is only by turning him from prayer that they can hinder his journey. What ever good work a man undertakes, if he perseveres in it, he will attain rest. But prayer is warfare to the last breath.’”
~From The Sayings of the Desert Fathers