The Heidelberg Catechism: Lord's Day 7
20. Questions: Are all men, then, saved by Christ just as they perished through
Answer: No. Only those are saved who by a true faith are grafted into Christ and accept all His benefits.
 Matt. 7:14; John 1:12; 3:16, 18, 36; Rom. 11:16-21.
21. Question: What is true faith?
Answer: True faith is a sure knowledge whereby I accept as true all that God has revealed to us in His Word. At the same time it is a firm confidence that not only to others, but also to me, God has granted forgiveness of sins, everlasting righteousness, and salvation, out of mere grace, only for the sake of Christ's merits. This faith the Holy Spirit works in my heart by the gospel.
 John 17:3, 17; Heb. 11:1-3; James 2:19.  Rom. 4:18-21; 5:1; 10:10; Heb. 4:16.  Gal. 2:20.  Rom. 1:17; Heb. 10:10.  Rom.3:20-26; Gal. 2:16; Eph. 2:8-10.  Acts 16:14; Rom. 1:16; 10:17; I Cor. 1:21.
22. Question: What, then, must a Christian believe?
Answer: All that is promised us in the gospel,  which the articles of our catholic and undoubted Christian faith teach us in a summary.
 Matt. 28:19; John 20:30, 31.
23. Question: What are these articles?
Answer: III.1.I believe in God the Father almighty, III.1. Creator of heaven and earth. III.2.I believe in Jesus Christ, III.2.His only begotten Son, our Lord; III.3.He was conceived by the Holy Spirit, III.3.born of the virgin Mary; III.4.suffered under Pontius Pilate, III.4.was crucified, dead, and buried; III.4.He descended into hell; III.5.On the third day He arose from the dead; III.6.He ascended into heaven, III.6.and sits at the right hand III.6.of God the Father almighty; III.7.from there He will come to judge III.7.the living and the dead. III.8.I believe in the Holy Spirit; III.9.I believe a holy catholic Christian church, III.9.the communion of saints; III.10.the forgiveness of sins; III.11.the resurrection of the body; III.12.and the life everlasting.
The Heidelberg Catechism: Lord's Day 6
16. Question: Why must He be a true and righteous man?
Answer: He must be a true man because the justice of God requires that the same human nature which has sinned should pay for sin. He must be a righteous man because one who himself is a sinner cannot pay for others.
 Rom: 5:12, 15; I Cor. 15:21; Heb. 2:14-16.  Heb. 7:26, 27; I Pet. 3:18.
17. Question: Why must He at the same time be true God?
Answer: He must be true God so that by the power of His divine nature He might bear in His human nature the
burden of God's wrath, and might obtain for us and restore to us righteousness and life.
 Is. 9:5.  Deut. 4:24; Nah. 1:6; Ps. 130:3.  Is. 53:5, 11; John 3:16; II Cor. 5:21.
18. Question: But who is that Mediator who at the same time is true God and a true and righteous man?
Answer: Our Lord Jesus Christ, whom God made our wisdom, our righteousness and sanctification and redemption (I Corinthians 1:30).
 Matt. 1:21-23; Luke 2:11; I Tim. 2:5; 3:16.
19. Question: From where do you know this?
Answer: From the holy gospel, which God Himself first revealed in Paradise. Later, He had it proclaimed by the patriarchs and prophets, and foreshadowed by the sacrifices and other ceremonies of the law. Finally, He had it fulfilled through His only Son.
 Gen. 3:15.  Gen. 12:3; 22:18; 49:10.  Is. 53; Jer. 23:5, 6; Mic. 7:18-20; Acts 10:43; Heb. 1:1.  Lev. 1:7; John 5:46; Heb. 10:1-10.  Rom. 10:4; Gal. 4:4, 5; Col. 2:17.
The Heidelberg Catechism
Lord's Day 1