All these things establish purity of heart; and it is for this that we should do everything, scorning possessions, enduring fasts and vigils gladly, engaging in spiritual reading and psalmody. If, however, some necessary task pleasing to God should keep us from our normal fasting and reading, we should not on this account neglect purity of heart. For what we gain by fasting is not so great as the damage done by anger; nor is the profit from reading as great as the harm done when we scorn or grieve a brother.
‘Fasts and vigils, the study of Scripture, renouncing possessions and everything worldly are not in themselves perfection, as we have said; they are its tools. For perfection is not to be found in them; it is acquired through them. It is useless, therefore, to boast of our fasting, vigils, poverty, and reading of Scripture when we have not achieved the love of God and our fellow men. Whoever has achieved love has God within himself and his intellect is always with God.’
– St. John Cassian quoting Abba Moses, The Philokalia as translated by Bishop Kallistos Ware, G.E.H. Palmer, and Philip Sherrard