Keep clean from the stain of mortal sin

"The first thing that a soul should do, is to keep herself clean from the stain of mortal sin, in such sort as to be sensible not to have upon her conscience any mortal offence which she has not confessed entirely: That she remain not in an uncertainty or scruple not to have declared every one sully in confession; so likewise must she have done some convenient suitable penance, and also make as often as possible most firm purposes and resolutions not to commit any sin though never so small, not for the whole world, nay, not if it should cost the life a hundred thousand times over. For if before we are arrived at this purity of conscience, we will force ourselves, or attempt to attain great perfection, we labour but in vain, for so long as we find ourselves terrified with any mortal sin, of which we endeavour not to dispossess ourselves by a salutary repentance, we shall never attain to the true Love of God, neither will perfection ever begin in our Hearts, so long as they are perplexed with remorse about sins, which we fear not to have so well conferred."

--  A Burning Lamp by Jerónimo de la Madre de Dios Gracián, ocd

** This is the same Fr Jerome Gratian that holy mother St Teresa loved so much.