…the servant of God must not content himself with any tiny relish of devotion he may experience in prayer, as some do who, having squeezed out a little tear, or felt some slight kindling of the heart, fancy they have fully accomplished this exercise.  Not thus is secured the end we are seeking.  Just as a little sprinkling of water…is of no use for enriching the soil, but plenty of water is needed to penetrate deep down and diffuse there the fertile moisture, so do we need an abundance of this dew and water from heaven if we are to bring forth the fruit of good works.  Hence we are advised, with good reason, to spend over this holy exercise as long a time as we are able, and better is one period of some length than two shorter ones; for where the time is short it is all taken up in controlling the imagination and tranquilizing the heart, and barely have we succeeded in doing this, than we finish the exercise at the very moment we ought to be beginning it.  In determining the length of time…anything less than an hour and a half or two hours is a short time to assign for prayer.  Often enough half an hour is spent in quieting down…the imagination and bringing the strings of our instrument into tune, and we want all the remainder of the time for relishing the fruit of prayer…..the heart is better disposed for this work, and, like dry wood, very much more quickly set aglow with the heavenly fire, when this exercise comes after some other holy exercise, like Matins, or after one has heard or said Mass, or after some devout reading or vocal prayer.  St Peter of Alcantara ‘Treatise on Prayer and Meditation’