The Seventh Commandment is: Thou shalt not steal. It obliges us to be honest in our dealings with our neighbor - to do to others as we would have them do to us. (Luke 6:13.) It forbids all unjust taking or keeping what belongs to another; or injuring another's property. Thus it forbids robbery, thieving and cheating. Robbery is taking by violence what belongs to another. Thieving is taking secretly what belongs to another. Cheating is deceiving another so that while he thinks he is getting a fair deal he is really being tricked; for example by getting rotten or damaged goods, or by being given wrong change.
Children cheating in examination may commit grave sin by depriving someone else of a prize, or scholarship. An employer who does not give a just wage sins against this Commandment, as well as a worker who idles away the time for which he is being paid to work. Small sins committed against this Commandment differ from others in this - that the matter can accumulate and finally become serious. Thus a man who constantly takes small things from his place of work, though each time he commits only venial sin, will be guilty of mortal sin as soon as the total amount he has stolen becomes sufficiently grave to make it a serious matter. A mortal sin is committed against justice when we do serious injury to our neighbor in his property. For example if you robbed a workman of a full day's wages, that would be a sufficiently grave injury to constitute a mortal sin.
The world of Holy Scripture: "He that despiseth small things shall fall by little and little," (Ecclus. 21:1.) are particularly true of justice. Jesus Christ warns us; "He that is unjust in that which is little, is unjust also in that which is greater." (Luke 16:10.) Never be willfully dishonest in the smallest matter if you wish to succeed, not only in the next world but also in this world. A thief is always sooner or later known and despised. "Honesty is the best policy" are words even of human wisdom.
Discarded property may be taken, as it is no longer wanted by the owner. Lost property may be retained, if the owner cannot be found, after making reasonable effort to locate him. Borrowed property must be restored, in the condition that it was borrowed. For example, if a car was borrowed with gas in the tank, then it should be returned with gas in the tank. Debts must be paid with a reasonable time. Stolen property, that is, property stolen by others, we must have nothing to do with; otherwise we become sharers in their sin. Restitution: If we have stolen or unjustly injured another's property, we must make restitution or compensation as far as lies in our power. Unless we have at least the sincere intention of restoring, our sin cannot be forgiven. Restitution as a general rule must be made to the owner of his heirs. If that is impossible, it may be made to some charity. But the thief may not retain his ill-gotten gains. In particular cases it is well to ask the advice of a confessor. The thought that sins against justice can never be forgiven while the stolen property is unjustly retained, should be a deterrent against yielding to any temptation to steal.
Rev. Fr. W. Frean, C.SS.R.
The Uselessness of Stolen Goods.
Stealing is forbidden because of the uselessness of stolen goods, for they are of no spiritual value: "Treasures of wickedness shall profit nothing." (Prov. 10:2.) Wealth can indeed be useful for alms-giving and offering of sacrifices, for "the ransom of a man's life are his riches." (Prov. 13:8.) It also should be known that a thief may lose not only his own soul, but also the souls of his children, since they too, are bound to make restitution.
St. Thomas Aquinas.