St. Teresa of Avila
The Way of Perfection
Chapter 22 · Part 2 of 2
Explains the meaning of mental prayer
Shall less respect be paid to Thee, then, my Spouse, than to men? If they think it unfitting to do Thee honour, let them at least leave Thee Thy brides, who are to spend their lives with Thee. A woman is indeed fortunate in her life if her husband is so jealous that he will allow her to speak with no one but himself; it would be a pretty pass if she could not resolve to give him this pleasure, for it is reasonable enough that she should put up with this and not wish to converse with anyone else, since in him she has all that she can desire. To understand these truths, my daughters, is to practise mental prayer. If you wish to learn to understand them, and at the same time to practise vocal prayer, well and good. But do not, I beg you, address God while you are thinking of other things, for to do that is the result of not understanding what mental prayer is. I think I have made this clear. May the Lord grant us to learn how to put it into practice. Amen.
Source: The Way of Perfection (CCEL)