Sloth or Acedia is one of the seven Capital Sins or Vices. Our Savior Himself gave this definition when speaking to St. Faustina about Lukewarm Souls on one occasion: There are souls who thwart My efforts (Diary 1682). Souls without love or devotion, souls full of egoism and selfishness, proud and arrogant souls full of deceit and hypocrisy, lukewarm souls who have just enough warmth to keep themselves alive: My Heart cannot bear this. All the graces that I pour out upon them flow off them as off the face of a rock. I cannot stand them because they are neither good nor bad (Diary 1702).
Here is a prayer to overcome Sloth and Lukewarmness.
O my God, I know well that so negligent a life as mine cannot please Thee. I know that by my lukewarmness I have closed the door to the graces which Thou dost desire to bestow on me. O my God, do not reject me, as I deserve, but continue to be merciful toward me, and I will make great efforts to amend and to arise from this miserable state. In the future, I will be more careful to overcome my passions and to follow Your inspirations; and never through slothfulness will I omit my duties, but will strive to fulfill them with greater diligence and fidelity. In short, I will from this time forward do all I can to please Thee, and will neglect nothing which I know to be pleasing to Thee.
Since Thou, O my Jesus, hast been so liberal with Thy graces toward me and have deigned to give Thy Blood and Thy Life for me, I am sorry for having acted with so little generosity toward Thee, Who are worthy of all honor and all love. But, O my Jesus, Thou knowest my weakness. Help me with Your powerful grace; in Thee I confide. O Immaculate Virgin Mary, help me to overcome myself and to become a saint. Amen.