The ninth commandment is “You shall not covet your neighbor’s wife.” This commandment is found within the larger formulation given in Exodus 20:17: “You shall not covet your neighbor’s house. You shall not covet your neighbor’s wife, his male or female slave, his ox or donkey, or anything that belongs to your neighbor.” This same verse forms the basis of the tenth commandment (regarding coveting the possessions of one’s neighbor). Here in the ninth it is coveting another’s spouse that is considered; and not unlike the sixth commandment the dignity of every person is implied.
In The New Saint Joseph Baltimore Catechism, the word “covet” is defined as “to wish to get a thing unjustly.” Minding that coveting another’s spouse is both a matter of envy and unchastity, this commandment seeks to treat both of these realms – even though the sixth commandment has already covered the realm of chastity with particular emphasis on marriage and the tenth will more directly cover envy of another’s abilities and material goods. The ninth commandment is especially focused upon being “pure of heart.” As Catechism of the Catholic Church, paragraph 2518 defines it the “’Pure of heart’ [are] those who have attuned their intellects and wills to the demands of God’s holiness, chiefly in three areas: charity; chastity or sexual rectitude; love of truth and orthodoxy of faith.”
To be “chaste” cannot be reduced to only include self-denial or abstinence – though such withholding of self has proper place in chaste living. True chastity (which is a fruit of the life in the Holy Spirit – as Paul tells us in Galatians 5:23, [though some bible translations use the expression “self-control”]) is a living in right relationship with every person, seeing each person for who they are in God’s eyes. The chaste person, therefore, lives true to his/her vocation by relating to every other person in the manner that is proper to one’s own state in life while upholding and respecting that of others. Thus, living out marital chastity (exclusive fidelity between spouses) clearly differs than celibate chastity, which differs still from being single, being in courtship, widowhood, etc. On the other hand, all states in life hold in common the need to see and relate to each person in the most proper way according to each one’s state in life – always with a pure heart.
Breaches of the ninth commandment, therefore, include immodesty (when that which is meant to be guarded in upholding one’s own dignity, often in the realm of appearance and how one presents one’s self, is not held sacred). While we are never to look at others as objects to be used for pleasure, proper modesty especially calls each one of us to express ourselves and our appearance in a manner that is becoming of our dignity, and never as an occasion of sin for others. Unfortunately, both of these sides of modesty – that is, from the viewpoint of the one who seeks pleasure from others and from the place of those with no regard for guarding their own dignity whose appearance becomes a source of temptation – are not well respected in our age and therefore make keeping this commandment all the more difficult.
Therefore, as we consider this very brief overview of the ninth commandment, the necessity of relying on God’s grace is made all the more evident. It is only by the help of God, given us especially through graces received in the sacraments, that we are able to uphold this way of purity of heart – through charity, chastity, and love of truth.
For further reading: In the Catechism of the Catholic Church, paragraphs 2514 – 2533 offer explanation of the ninth commandment, with primary attention on purity of heart and modesty.