The Heidelberg Catechism: Lord's Day 45
116. Question: Why is prayer necessary for Christians?
Answer: Because prayer is the most important part of the thankfulness which God requires of us. Moreover, God will give His grace and the Holy Spirit only to those who constantly and with heartfelt longing ask Him for these gifts and thank Him for them.
 Ps. 50:14, 15; 116:12-19; I Thess. 5:16-18.  Matt. 7:7, 8; Luke 11:9-13.
117. Question: What belongs to a prayer which pleases God and is heard by Him?
Answer: First, we must from the heart call upon the one true God only, who has revealed Himself in His Word, for all that He has commanded us to pray. Second, we must thoroughly know our need and misery, so that we may humble ourselves before God. Third, we must rest on this firm foundation that, although we do not deserve it, God will certainly hear our prayer for the sake of Christ our Lord, as He has promised us in His
 Ps. 145:18-20; John 4:22-24; Rom. 8:26, 27; James 1:5; I John 5:14, 15; Rev. 19:10.  II Chron. 7:14; 20:12; Ps. 2:11; 34:18; 62:8; Is. 66:2; Rev. 4.  Dan. 9:17-19; Matt. 7:8; John 14:13, 14; 16:23; Rom. 10:13; James 1:6.
118. Question: What has God commanded us to ask of Him?
Answer: All the things we need for body and soul, as included in the prayer which Christ our Lord Himself taught us.
 Matt. 6:33; James 1:17.
119. Question: What is the Lord's prayer?
Answer: Our Father who art in heaven, Hallowed be Thy Name. Thy kingdom come, Thy will be done, On earth as it is in heaven. Give us this day our daily bread; And forgive us our debts, As we also have forgiven our debtors; And lead us not into temptation, But deliver us from the evil one. For Thine is the kingdom, and the power, and the glory, for ever. Amen.
 Matt. 6:9-13; Luke 11:2-4.
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.