[Amma Syncletica said] ‘It is dangerous for anyone to teach who has not first been trained in the “practical” life. For if someone who owns a ruined house receives guests there, he does them harm because of the dilapidation of his dwelling. It is the same in the case of someone who has not first built an interior dwelling; he causes loss to those who come. By words one may convert them to salvation, but by evil behaviour, one injures them.’
The Sayings of the Desert Fathers. The Alphabetical Collection, translated by Benedicta Ward, SLG, (Kalamazoo: Cistercian Publications, 1975 ) 233.
And, on a similar note,
If you wish to sow your seed among the destitute, sow from your own seed; for if you wish to sow from the seed of others, know that what you sow is the most bitter of tears.
Abba Nilos of Sinai, as quoted by Saint Isaac of Nineveh, The Ascetical Homilies of Saint Isaac the Syrian, translated by the Holy Transfiguration Monastery, Boston, 1984. 30.