"God certainly gives us the grace to overcome our evil tendencies; but we must also use our own efforts, which consist in voluntary mortification: 'They that are Christ's have crucified their flesh, with the vices and concupiscences.' (Galatians 5:24) The purpose of corporal mortification is not to inflict pain and privation on the body for the pleasure of making it suffer, but to discipline and control all its tendencies which are contrary to the life of grace.
"We must curb ourselves in order to avoid falls; we must prune the useless or harmful branches n order to avoid deviation; we must direct toward good the forces which, left to themselves, might lead us into sin. For these reasons mortification, although it is not an end in itself nor the principal element in the Christian life, occupies a fundamental place in it and is an absolutely indispensable means toward attaining a spiritual life. No one can escape this law without closing off all access to eternal salvation, to sanctity.
"St. Teresa warns us that 'if prayer is to be genuine it must be reinforced with this practice of mortification, for prayer and self-indulgence do not go together.' It would be an illusion to think that we can reach intimacy with God without the serious exercise of physical mortification. In this regard, we must take care that love of our body and of our physical welfare does not cause us to reject all penitential practices under the pretext that they will ruin our health. In reality, there are many corporal mortifications which, without the slightest danger to our health, have the great advantage of keeping our spirit of generosity on the alert by the voluntary acceptance of a little physical suffering. If we are to be generous in this respect, we must 'rid ourselves of all inordinate love for our body,' that is, of all excessive preoccupation about our health; and we must put aside all anxiety about food, clothing, rest and comfort. 'This body of ours,' says St. Teresa, 'has one fault: the more you indulge it, the more things it discovers to be essential to it...and if there is any reasonable pretext for indulgence, however little necessity for it there may be, the poor soul is deceived and prevented from making progress.'
"Anyone who wants to advance on the road to sanctity and union with God must be ready to sacrifice everything, even in the physical order, to the point of 'giving up his skin and everything else for Christ,' as St. John of the Cross says.
"This is the predominant thought of the day. We read in the Epistle (Joel 2:12-19), 'Thus saith the Lord: be converted to Me with all your heart, in fasting and in weeping and in mourning. And rend your hearts, and not your garments.' Compunction and conversion of heart hold the first place, because the corporal penance that does not proceed from a contrite heart has no value. On the other hand, corporal penance prepares the soul for conversion, insofar as it is the means of reaching it. We read in the Preface, 'O God, by fasting You repress sin, elevate the soul, and give it strength and recompense.' One who wishes to reach the goal, which is the renewing of the spirit, must embrace willingly the means which leads to it, namely, corporal penance. At the same time, he must remember that compunction of heart gives value to corporal penance, which in its turn engenders and gives expression to compunction of heart. The two elements are never separated.
"The Gospel (Matthew 6:16-21) says further that all penance must be accomplished sincerely and joyfully, without vain ostentation. 'When you fast, be not as the hypocrites, sad. For they disfigure their faces, that they may appear unto men to fast.' Vanity and pride make even the most austere penitential practices useless and sometimes even sinful; they destroy their substance and value, and reduce them to mere externals, empty of all content. Hence when you mortify your body, take care to mortify your self-love still more."
-reflections from Divine Intimacy by Father Gabriel of St. Mary Magdalen, O.C.D.