All men are under obligation to make reparation

"Among the various devotions paid to the Sacred Heart, the one foremost in importance and interest is assuredly the Act of Consecration, whereby we give to the divine Heart of Jesus both ourselves and all that is ours; in recognition of the truth that all we have cometh unto us out of the infinite charity of the eternal Deity.  But it is expedient that any attempt of ours at self-consecration be accompanied with the purpose of making expiation (otherwise called reparation) to the most Sacred Heart of Jesus.  In consecration the predominant intention may be said to be the purpose to repay (as it were) the love of the Creator by the love of us his creatures.  But since Love Uncreate is passed over by human forgetfulness, and dishonoured by the sins of mankind, we should endeavour to repair such outrages; and the performance of this duty is ordinarily known as reparation.

If we are, for the aforesaid reasons, to undertake both of those practices, we must recognize that we are impelled to the duty of reparation by the most powerful motives of justice and love: of justice, in order to expiate the injury done to God by our sins, and to re-establish through penance the divine order which was violated by them; of love, in order to suffer together with Christ, (who patiently endured all possible dishonour,) so that we may offer him some solace in return for his sufferings.  For it is our duty to do more than honour God by the worship of adoration, whereby we adore his infinite Majesty, or by means of prayer, when we recognize his supreme dominion over us, or by acts of thanksgiving, when we praise his infinite generosity towards us.  Because we are sinners, burdened with many offences, we must also make satisfaction to the offended justice of God, because of the numberless sins, offences and negligences we have committed.  Wherefore, we must add to the act of consecration, by which we offer ourselves to God, and become thereby, as it were, sacred unto God by reason of the holiness which naturally floweth from an act of consecration, as the Angelic Doctor teacheth.  We must add the act of reparation, by means of which all our faults are blotted out, lest perchance the sanctity of Infinite Justice spurn our arrogant unworthiness, and look upon the gift of ourselves as something to be rejected rather than accepted.

All men are under obligation to make reparation; for our souls are disfigured as the Christian faith teacheth by original sin as a result of the pitiable fall of Adam.  We are also subject to passions, whereby we are corrupted in a truly sad state, and have thus made ourselves worthy of everlasting condemnation.  It is true that the proud philosophers of this world deny the aforesaid verities, and in their place do raise up again the ancient heresy of Pelagius: which taught that in human nature there is a certain innate goodness wherewith, by our own powers, we are raised up to ever higher levels of perfection; but such false theories, born of human pride, have been condemned by the Apostle in his saying that all men are by nature the children of wrath.  As a matter of fact, from the very beginning of the creation of the world, mankind recognized, in one way or another, the obligation of making reparation, impelled thereto, as by a natural instinct, in an endeavour to placate God by offering public sacrifices unto him."

-- From the Encyclical Letter of Pope Pius XI