Fret not thyself, it tendeth only to evil-doing.
Ps. xxxvii. 8 (R. V.).

To anxious, prying thought,
And weary, fretting care.
The Highest yieldeth nought;
He giveth all to prayer.
Paul Gerhardt.

DO not be disquieted about your faults. Love without ceasing, and much will be forgiven you, because you have loved much. Faults perceived in peace, in the spirit of love, are immediately consumed by love itself; but faults perceived in a pettish fit of self-love disturb peace, interrupt the presence of God, and the exercise of perfect love. Vexation at a fault is generally more of a fault than the fault itself.
FRANCOIS DE LA MOTHE FENELON.

Fight like a good soldier; and if thou sometimes fall through frailty, take again greater strength than before, trusting in my more abundant grace.
Thomas A. Kempis.

This alone is thy concern, to fight manfully, and never, however manifold thy wounds, to lay down thine arms, or to take to flight.
Lorenzo Scupoli