“Our whole life ought to be one continued penance“.

Joel 2:12: “Yet even now,” says the Lord,
    “return to me with all of your heart,
with fasting, weeping, and with mourning“

“But if the wicked do penance. . . . .I will not remember all his iniquities.”—Ezek.xviii.21

The Nature and the Necessity of Penance

As soon as the fish swallows the bait, he feels the smart. So it is with the sinner. Yet what God has laid upon us as a chastisement He has made the means of our salvation; He sends suffering as the chastisement of sin; but by suffering we can be delivered from sin.

Interior sorrow for sin, accompanied by sincere turning from creatures and turning to God, is generally called penance.

As a matter of fact, our whole life ought to be one continued penance.

Our Lord says: “Unless you shall do penance, you shall all likewise perish” ( Luke xiii. 3 ). And again: “Woe to you that now laugh, for you shall mourn and weep” ( Luke vi. 25 ).

He often threatens those who only desire to enjoy life, with eternal perdition ( John xii. 25 ). No man, even should he not be conscious of any sin, ought to depart out of this world without doing penance (St. Augustine).

St. Jerome says we can no more attain everlasting life without penance, than we can get at the kernel of a nut without breaking the shell. The greatest saints used to perform severe penances for their slightest faults.

Confession

Our Lord instituted the Sacrament of Penance on the day of His resurrection, when He spoke these words to His apostles:

“Whose sins you shall forgive, they are forgiven; and whose sins you shall retain, they are retained” ( John xx. 23 ).

With these words Christ on the one hand imparted to the apostles the power to remit sins, and on the other laid upon the faithful the injunction to confess their sins to a priest in order to obtain the remission of them. The conditions under which forgiveness of sins is to be obtained, are indicated in the following instances:

(1), the cure of the man sick of the palsy ( Matt . ix. ); sin is a spiritual paralysis; when sin is forgiven, a penance is imposed on the penitent, as the paralytic was commanded to carry his bed;

(2), The cleansing of the leper ( Matt . viii. ); sin is a spiritual leprosy; the sinner must show himself to the priest, who will declare him to be clean by God’s authority;

(3), The absolving of the penitent Magdalen, who cast herself at Our Lord’s feet, and heard from His lips the words: “Thy sins are forgiven thee” ( Luke vii. ). The sinner now acts as she did; filled with contrition, he casts himself at the feet of Christ’s representative, and obtains the pardon of his transgressions.

… The Sacrament of Penance is indispensably necessary for those who have fallen into sin after Baptism, for without this sacrament they are unable to recover the justice they have lost (Council of Trent, 14, 1; 6, 29).

“The Sacrament of Penance is, for those who have fallen after Baptism, as necessary unto salvation as Baptism itself is for those who have not yet been regenerated” (Council of Trent, 14, 2).

Hence the Fathers term this sacrament: “the second baptism,” or “the plank after shipwreck.”

— from The Catechism Explained, An Exhaustive Explanation of the Christian Religion: Cross-linked to the Bible” by Frs. Francis Spirago, Richard F. ClarkeThe Catechism Explained

St. Alphonsus de Liguori

“Would that sinners only knew how mercifully our Saviour awaits them in order to pardon them: ‘The Lord waits that He may have mercy upon you’ (Isaiah 30:18).

Would that sinners realised the desire on the part of God, not, indeed, to chastise them, but to see them converted and to embrace and press them to His Heart: ‘As I live, says the Lord God, I desire not the death of the wicked, but that the wicked turn from his way and live’ (Ezekiel 33:11).

He has even still more consoling words: ‘Come and accuse Me, says the Lord; if your sins be as scarlet, they shall be made as white as snow’ (Isaiah 1:18). In other words, He says: ‘Sinners, repent of having offended Me and then come to Me. If I do not pardon you, accuse Me of being unfaithful to My promises; but, no, I will keep My word. If you come to Me and repent, though your soul be dyed deep crimson with crime, by My grace it shall be made white as snow.’

Almighty God promises even to forget the sinner’s wrong-doing if only he repents: ‘I will not remember all his iniquities’ (Ezekiel 18:22).

As soon, then, as you fall into any fault, raise your eyes to God, make an act of love, and humbly confessing your fault, place unwavering confidence in God, saying to Him: ‘Lord, behold, he whom You love is sick’ (John 11:3). The heart which You love is sick—is wounded. ‘Heal my soul, for I have sinned against You.’ (Psalm 41:4 in the Hebrew or, in the Vulgate, Psalm 40:5). — How to pray at all times