The Heidelberg Catechism: Lord's Day 8
24. Question: How are these articles divided?
Answer: Into three parts: the first is about God the Father and our creation; the second about God the Son and our redemption; the third about God the Holy Spirit and our sanctification.
25. Question: Since there is only one God, why do you speak of three persons, Father, Son, and Holy Spirit?
Answer: Because God has so revealed Himself in His Word that these three distinct persons are the one, true, eternal God.
 Deut. 6:4; Is. 44:6; 45:5; I Cor. 8:4, 6.  Gen. 1:2, 3; Is. 61:1; 63:8-10; Matt. 3:16, 17; 28:18, 19; Luke 4:18; John 14:26; 15:26; II Cor. 13:14; Gal. 4:6; Tit. 3:5, 6.
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.