I've added Br. Thomas's description of Seven Principles of the Spiritual Life to the website. The principles, based on the teaching of St. Thomas Aquinas and St. Therese of Lisieux, are the following:
1. To keep God in mind at all times.
2. To trust in God as much as possible.
3. To do all things for the love of God.
4. Not to trust in oneself.
5. Not to seek oneself.
6. To do all things with joy.
7. To be as energetic as possible.
The sixth and seventh principles may be a bit of a surprise. Is it even in our power to do things with joy? What does "energy" have to do with spiritual life? Yet St. Paul tells us to "Rejoice in the Lord always" (Phil 4:4), and St. Therese says that energy "is the most necessary virtue; with energy one can easily reach the height of perfection" (LT 178). These and the other principles are explained at greater length in the article. Comments are welcome!
While sin itself is always bad, for the sinner who sincerely repents, and turns to God who forgives the sin, it can be the occasion of joy over the mercy and love of God that are revealed in his forgiveness of it.
St. Thérèse of Lisieux apparently went so far as to say that the lovers of God "take delight" in their indeliberate faults, inasmuch as they show God's mercy.
"The rest of us don't belong among those saints who cry over our sins: we take delight in them because they serve to glorify the mercy of God." (Words of St. Thérèse recollected by Sr. Marie of the Trinity.)
And her sorrow for the sin itself, she offers to God as a sign of her love for him.
"When I have committed a fault that makes me sad, I know well that this sadness is the consequence of my infidelity. But do you think I stop there? Oh no, I'm not so silly! I hurry to say to God: My God, I know that I have merited this feeling of sadness, but let me offer you all of it as a test that you send me out of love. I regret my sin, but I am content to have this suffering to offer to you. (Words of St. Thérèse recollected by Sr. Agnes of Jesus.)
Sayings of St. Therese on love
"Rejoice in the Lord always; again I will say, Rejoice. Let all men know your forbearance. The Lord is at hand. Have no anxiety about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God" (Philippians 4:4-6).
Most of the time anxiety is not particularly helpful. The purpose of anxiety is to make us alert and ready to avoid some danger. But when there's nothing we can do to avoid the evil we're afraid of, when it's not reasonable for us to take many steps to avoid it, or in general when this being-on-guard against danger is useless, there's no point in being anxious. It takes away peace, and hinders us from a wholehearted and joyful pursuit of the good we are about. An recent example occurred, in which someone on a pilgrimage was anxious about reaching a Mass on time. The judgment that they should walk more quickly might be a reasonable one, but after making such a judgment, and increasing the pace, there is no point in worrying more about the matter.
But how to avoid such anxiety? One important step is to mentally accept the potential bad outcome about which one is tending to worry. If there is nothing more one can to do avoid it, it is perfectly legitimate to accept it as if it already happened. Another step, more relevant to the passage quoted from St. Paul, is to look at the matter in light of God's providence. The present situation is within God's providence, as well as the outcome, whether that turn out to be what one is hoping for, or the contrary. St. Francis de Sales states, as a general principle, that we should do what we can to attain good results, but leave the result in God's hand, as in fact it is. As we accustom ourselves to seeing God's hand in everything, this reliance on God will naturally lessen worry and anxiety, without in any way diminishing our care to fulfill our duties.
See also sayings of St. Therese on love