Book 1, Chapter 19: On the Spiritual Exercise of the Devout Disciple
Comment: Chapter 19
Spiritual exercises help us get strong and stay healthy in our faith walk: prayer, fasting, corporal and spiritual works of mercy, and so on. Everyone has different needs and capabilities in this area. Regardless, Thomas calls us out to be transparent in our spiritual progress. Such exercises are not to be lightly 
omitted. The right exercises will help us to develop “spiritual muscles” in all the right places, especially in warding off temptation. Finally, when the calendar rolls to especially holy seasons (think Advent, Christmas, Lent, Easter), we should adjust and increase our spiritual practices in accordance with the seasons.
This chapter contains a quote for which Thomas is often cited:
Man proposes and God disposes.
In the spiritual life, this simply means that when we are set to try something, many other items develop which keep us from accomplishing that task – God is in control.
Chapter 19 In Short.
1. Let your outward life reflect your inward life. Renew your vows daily with the zeal of a new convert.
2. The rate of our spiritual progress is determined according to our goals, however, ”Man proposes but God disposes.”
3. Do not omit spiritual exercises lightly.
4. Make time to examine yourself twice daily. Be aware of your temptations. Don’t be spiritually idle.
5. Faithfully discharge the duties given to you, if you have leisure time, use it for self-directed devotion.
6. By prayerful renewal, prepare for the solemn seasons.
7. Blessed is that servant, whom, when the Lord comes He shall find watching.
Book 1, Chapter 19: On the Spiritual Exercises of the Devout Disciple
The life of a Christian ought to be adorned with all virtues. The disciple should therefore be inwardly what is demonstrated outwardly to others.
And truly it should be even better within than without, for God is a discerner of our hearts, Whom we must reverence with all our hearts wherever we are, and walk pure in His presence as do the angels.
We ought daily to renew our vows, and to kindle our hearts to zeal, as if each day were the first day of our conversion, and to say to Him:
“Help me, O God, in my good resolutions, and in Your holy service, and grant that this day I may make a good beginning, for prior to this I have done nothing!”
2. The rate of our spiritual progress is determined according to our resolution, and diligence is required for that disciple who would make good progress. It is better if you resolve bravely and fall short, than to make rare or feeble resolutions.
Man Proposes, God Disposes
But many things happen to bring about the abandonment of our resolution – yet a trivial omission of holy exercises can hardly be made without some loss to us. The resolution of the righteous depends more upon the grace of God than upon their own wisdom; for in Him they put their trust, whatever they take in hand. For man proposes, but God disposes. And the way of a man is not in himself (Jer 10:23).
3. If spiritual exercises are sometimes omitted for the sake of some act of piety, or of some kindness, it can easily be taken up afterwards; but if these practices are neglected because of discomfort or laziness, then this is sinful, and harmful.
Strive as earnestly as we may, we still fall short in many things. We should always make some distinct resolution; and, most of all, we must strive against those sins which most easily beset us. Both our inner and outer life should be thoroughly examined and ruled by us, because both have to do with our progress.
4. If you cannot always be examining yourself, you can do so at appointed times, and at least twice in the day, at evening and at morning. In the morning make your resolutions, and in the evening inquire into your life, how you have spent today in word, deed, and thought; for in these ways you have often possibly offended God and your neighbor.
Gird up your loins against the assaults of the devil; bridle your appetite, and you will soon be able to bridle every inclination of the flesh. Never be wholly idle; but be doing something: be it reading, or writing, or praying, or meditating, or something that is useful to the community. Bodily exercises, however, must be undertaken with discretion, nor are these to be used by all in the same way.
5. The duties which are not common to all must not be done openly, but are most safe when carried on in secret. But take heed to not become careless in your common duties, and more devout in the secret; but faithfully and honestly discharge the duties and commands which lie upon you, then afterward, if you still have leisure, give yourself to yourself as your devotion leads you.
Not all can have the same exercise: one is suited better to this disciple and another to that one. At different seasons different exercises are needed, some are suited better for feasts, some for fasts. We need one kind of exercise in time of peace and quietness and another in a time of temptation. Some are suitable to times of sadness, and others when we are joyful in the Lord.
6. When we draw near the time of the great feasts, good exercises should be renewed, and the prayers of the holy ones more fervently sought out. We ought to make our resolutions from one Feast to another, as if each were the period of 
our departure from this world, and of entering into the eternal feast. So we ought to prepare ourselves fervently during the solemn seasons, and likewise live more solemnly. We should keep purest watch on each holy observance, as though we were soon to receive the reward of our labors at the hand of God.
7. And if this is deferred, let us believe ourselves to be ill-prepared, and not yet worthy of the glory which shall be revealed to us at the appointed season; and let us study to prepare ourselves better for our life’s end.
Blessed is that servant, as the Evangelist Luke has it, whom, when the Lord
comes He shall find watching. “Truly, I say to you He will make him ruler over all that He has (Lk 12:43,44).”