Q. 113. What doth the tenth commandment require of us?
That even the smallest inclination or thought, contrary to any of God’s commandments, never rise in our hearts; but that at all times we hate all sin with our whole heart, and delight in all righteousness.
 Romans 7:7, &c.
Q. 114. But can those who are converted to God perfectly keep these commandments?
No: but even the holiest men, while in this life, have only a small beginning of this obedience; yet so, that with a sincere resolution they begin to live, not only according to some, but all the commandments of God.
 Romans 7:14;  Romans 7:22, 15, &c., James 3:2.
Q. 115. Why will God then have the ten commandments so strictly preached, since no man in this life can keep them?
First, that all our lifetime we may learn more and more to know our sinful nature, and thus become the more earnest in seeking the remission of sin, and righteousness in Christ; likewise, that we constantly endeavour and pray to God for the grace of the Holy Spirit, that we may become more and more conformable to the image of God, till we arrive at the perfection proposed to us, in a life to come.
 1 John 1:9; Romans 3:20 and 5:13 and 7:7;  Romans 7:24;  1 Corinthians 9:24; Philippians 3:12–14.
The Tenth Commandment, “Thou shalt not covet thy neighbour’s house, thou shalt not covet thy neighbour’s wife, nor his manservant, nor his maidservant, nor his ox, nor his ass, nor any thing that is thy neighbour’s,” condemns the sin of covetousness or the lack of contentment in the lot that God has assigned to us. It is the nature of it that is emphasised in the catechism, however, for it makes it explicit that the Ten Commandments must not only be kept externally but in our hearts and minds. From the testimony of the Apostle Paul, it appears that it was particularly this aspect of the Ten Commandments that pressed upon his conscience at his conversion. For he says: “I had not known sin, but by the law: for I had not known lust, except the law had said, Thou shalt not covet. But sin, taking occasion by the commandment, wrought in me all manner of concupiscence. For without the law sin was dead. For I was alive without the law once: but when the commandment came, sin revived, and I died” (Rom 7:7–9). Perhaps the Apostle Paul had felt that he was keeping sufficiently perfectly all the laws, because he was keeping them with external religious rigour. But the Tenth Commandment deals with what is entirely in the heart. There is no external performance required that may blind one into thinking that he is keeping it. Therefore once the heart is illumined by the Spirit of Christ and shown to be deceitful and desperately wicked, it becomes immediately obvious that no mere man can keep the Tenth Commandment. And if we can’t keep this (as it were) least of the Commandments, how could we be said to be keeping all the rest of the Commandments with our whole heart, soul, mind and strength (Mk 12:30)?
In other words, the Ten Commandments display our wickedness rather than our righteousness. It tells us how we ought to live, not because we are able to obey it perfectly, but because it is a standard God has set for us, and because it shuts us up to Christ for cleansing of sin and strength to live unto God.
Heidelberg Catechism >