“You shall not covet your neighbor’s goods.” There is this difference between the divine and the human laws that human law judges only deeds and words, whereas the divine law judges also thoughts. The reason is because human laws are made by men who see things only exteriorly, but the divine law is from God, who sees both external things and the very interior of men. “You are the God of my heart” [Ps 72:26]. And again: “Man sees those things that appear, but the Lord sees the heart” [1 Sam 16:7]. Therefore, having considered those Commandments which concern words and deeds, we now treat of the Commandments about thoughts. For with God the intention is taken for the deed, and thus the words, “You shall not covet,” mean to include not only the taking by act, but also the intention to take. Therefore, it says: “You shall not even covet your neighbor’s goods.” There are a number of reasons for this.
The first reason for the Commandment is that man’s desire has no limits, because desire itself is boundless. But he who is wise will aim at some particular end, for no one should have aimless desires: “A covetous man shall not be satisfied with money” [Eccles 5:9]. But the desires of man are never satisfied, because the heart of man is made for God. Thus, says St. Augustine: “You hast made us for You, O Lord, and our heart is restless until it rests in You” [Conf. I]. Nothing, therefore, less than God can satisfy the human heart: “He satisfies your desire with good things” [Ps 102:5].
The second reason is that covetousness destroys peace of heart, which is indeed highly delightful. The covetous man is ever solicitous to acquire what he lacks, and to hold that which he has: “The fullness of the rich will not suffer him to sleep” [Eccles 5:11]. “For where your treasure is, there is your heart also” [Mt 6:21]. It was for this, says St. Gregory, that Christ compared riches to thorns [Lk 8:14].
Thirdly, covetousness in a man of wealth renders his riches useless both to himself and to others, because he desires only to hold on to them: “Riches are not fitting for a covetous man and a niggard” [Sir 14:3].
The fourth reason is that it destroys the equality of justice: “Neither shall you take bribes, which even blind the wise, and pervert the words of the just” [Ex 23:8]. And again: “He who loves gold shall not be justified” [Sir 31:5].
The fifth reason is that it destroys the love of God and neighbor, for says St. Augustine: “The more one loves, the less one covets,” and also the more one covets, the less one loves. “Nor despise your dear brother for the sake of gold” [Sir 7:20]. And just as “No man can serve two masters,” so neither can he serve “God and mammon” [Mt 6:24].
Finally, covetousness produces all kinds of wickedness. It is “the root of all evil,” says St. Paul, and when this root is implanted in the heart it brings forth murder and theft and all kinds of evil. “They that will become rich, fall into temptation, and into the snare of the devil, and into many unprofitable and hurtful desires which drown men in destruction and perdition. For the desire of money is the root of all evil” [1 Tim 6:9-10]. And note, furthermore, that covetousness is a mortal sin when one covets one’s neighbor’s goods without reason; and even if there be a reason, it is a venial sin.