Treatise on the Love of God

Now as zeal is an inflamed ardour, or an ardent inflaming of love, it requires to be wisely and prudently practised; otherwise, under the cloak of it, one would transgress the limits of moderation or discretion, and it would be easy to pass from zeal into anger, and from a just affection to an unjust passion; wherefore, this not being the proper place to put down the conditions of zeal, my Theotimus, I tell you that for the practice of it you must always have recourse to him whom God has given you for your direction in the devout life.