The Heidelberg Catechism: Lord's Day 44
113. Question: What does the tenth commandment require of us?
Answer: That not even the slightest thought or desire contrary to any of God's commandments should ever arise in our heart. Rather, we should always hate all sin with all our heart, and delight in all righteousness.
 Ps. 19:7-14; 139:23, 24; Rom. 7:7, 8.
114. Question: But can those converted to God keep these commandments perfectly?
Answer: No. In this life even the holiest have only a small beginning of this obedience. Nevertheless, with earnest purpose they do begin to live not only according to some but to all the commandments of God.
 Eccles. 7:20; Rom. 7:14, 15; I Cor. 13:9; I John 1:8.  Ps. 1:1, 2; Rom. 7:22-25; Phil. 3:12-16.
115. Question: If in this life no one can keep the ten commandments perfectly, why does God have them preached so strictly?
Answer: First, that throughout our life we may more and more become aware of our sinful nature, and therefore seek more eagerly the forgiveness of sins and righteousness in Christ. Second, that we may be zealous for good deeds and constantly pray to God for the grace of the Holy Spirit, that He may more and more renew us after God's image, until after this life we reach the goal of perfection.
 Ps. 32:5; Rom. 3:19-26; 7:7, 24, 25; I John 1:9.  I Cor. 9:24; Phil. 3:12-14; I John 3:1-3.
The Heidelberg Catechism
Lord's Day 1