Sin is the opposite of holiness. Sin is saying "No" to God, and is the worship of a false god, ultimately ourselves. Sin means wasting the inheritance of God's love and grace like the prodigal son, and ending up in the pig-pen of our own emptiness. The prodigal son rightly said, "I have sinned against heaven and against you", because every sin, while it may be directed against ourselves or our neighbor, is also against God, the source of all life, all goodness and all truth. Pope Saint Paul John II wrote, "To sin is also to live as if God did not exist, to eliminate him from one's daily life." (Reconciliatio et Paenitentia 18)

The same saint wrote about the "loss of the sense of sin". "It is impossible to completely loose the sense of sin. Yet there is still a great danger. "Is it not true that modern man is threatened by ....a numbness or 'deadening' of conscience?" (Reconciliato et Paenitentia 18)   Pope Pius XI even declared that "the sin of the century is the loss of the sense of sin."

One reason for the loss of the sense of sin is the false idea that guilt is bad. But it is a healthy body which can feel pain and a healthy soul which can feel guilt. These two kinds of pain save us from danger to body and soul. The right way to cure the pain is not denial but repentance. Another reason for the loss of the sense of sin is making excuses for sin (rationalizing). This can lead to 'relativism', thinking that nothing is always (intrinsically) good or bad. For example, to say that lying is sometimes justified is at the same time saying that truth doesn't always matter, that truth isn't good in itself. This is a path to thinking nothing matters, good or bad. A person who thinks like that no longer really believes in goodness and so is no longer able to love.

Bad moral theology is full of rationalizing. It also falls into an exaggeration, as Saint Paul John  pointed out: "From (the exaggeration of) seeing sin everywhere they pass to not recognizing it anywhere; from too much emphasis on the fear of eternal punishment they pass to preaching a love of God that excludes any punishment deserved by sin; from the severity in trying to correct erroneous consciences they pass to a kind of respect for conscience which excludes the duty of telling the truth. (Reconciliato et Paenitentia 18)

Martyrs powerfully proclaim that there is such a thing as truth, as goodness, something worth living and dying for.  "The Church proposes the example of numerous Saints who bore witness to and defended moral truth even to the point of enduring  martyrdom, or who preferred death to a single mortal sin....Martyrdom.....bears splendid witness both to the holiness of God's law and to the inviolability of the personal dignity of man, created in God's image and likeness. Martyrdom is an outstanding sign of the holiness of the Church. The martyrs and, in general, all the Church's Saints, light up every period of history by reawakening its moral sense. (Veritatis Splendor 91-93)

In the parable of the tax collector and the Pharisee, Jesus taught us the value of humbly acknowledging our sins. The tax collector, not daring to raise his eyes, prays, "Lord, be merciful to me a sinner". He was heard because he acknowledged his sins from his heart. The tax collector was on the road to holiness, the Pharisee was not.

Source Catholic Contact