The brethren asked Abba Agathon: “Amongst all our different activities, father, which is the virtue that requires the greatest effort?” He answered: “Forgive me, but I think there is no labor greater than praying to God. For every time a man wants to pray, his enemies the demons try to prevent him; for they know that nothing obstructs them so much so much as prayer to God. In everything else that a man undertakes, if he perseveres, he will attain rest, but in order to pray a man must struggle to his last breath.”
Saying of the Desert Father, quoted in The Divine Hours: Prayers for Springtime, compiled by Phyllis Tickle