The phrase needs more context to be fully understood.
CCC2515: Etymologically, “concupiscence” can refer to any intense form of human desire. Christian theology has given it a particular meaning: the movement of the sensitive appetite contrary to the operation of human reason. The apostle St. Paul identifies it with the rebellion of the “flesh” against the “spirit”. Concupiscence stems from the disobedience of the first sin. It unsettles man’s moral faculties and, ** without being in itself an offense, inclines man to commit sins.**
Also, notice in the CCC1849 you quote there is a footnote : 121
which references the source of the definition which isn’t the catechism, there are two sources:
#1: St. Augustine: Against Faustus (the Manichee)
Sin, then, is any transgression in deed, or word, or desire, of the eternal law. And the eternal law is the divine order or will of God, which requires the preservation of natural order, and forbids the breach of it.
#2: St Thomas, Summa Theologica I-II, 71 #6
and to understand Thomas, you will need more Thomas!
I like Augustine’s original statement better, as it is simple.
br.joe brings up a good point concerning the Decalogue – which is a shorthand for the law of conscience inscribed in everyone’s heart (whether suppressed or not).
If you don’t want to slog throgh all of St. Thomas’ opinions, consider the summary given by Augustine after describing the difference between animals and man, desire and will.
A man, therefore, who acts in obedience to the faith which obeys God, restrains all mortal affections, and keeps them within the natural limit, regulating his desires so as to put the higher before the lower. If there was no pleasure in what is unlawful, no one would sin. To sin is to indulge this pleasure instead of restraining it.
Notice the second definition of sin.
The first definition, quoted by the CCC involves a transgression – which is a willful crossing the line of the law.
Sin is a word which simply means, straying from the intended (straight line) path. I am not certain of the Latin distinctions between sin, transgression, iniquity, and so forth – but the Greek treats sin as a state (noun) – and not always a guilt resultant on action.
Neither the true arrow (euthaphro) nor the stray arrow (amartia/sin) is at it’s target during the journey – but to follow the straight and narrow path at the end point is required to hit the target (God’s plan for us).
Augustine, in English translation (at least) tends to use sin as synonymous with willful transgression – and so one has to be careful to look for the circumstances of the sin to know whether or not it involves guilt, and to what degree (venial/Mortal). Notice that as a verb “to sin” rather than a noun “sin” it may imply the will of the person to be off the straight path.
– So to paraphrase Jesus: to look upon a woman in order to lust (desire/covet) her is to have committed adultery in your heart.
The will is set to actively FIND a woman to look at IN ORDER to lust, is a sin – because the heart has made the decision to sin, and is simply searching for a way to do it.
That is different from being hit by a passion (concupiscence) because a scantily clad woman chooses to walk into view – eg: the beer commercials… etc.