The Heidelberg Catechism Part II: Deliverance Lord’s Day 8
Question 24: How are these articles divided?
Answer 24: Into three parts: God the Father and our creation; God the Son and our deliverance; and God the Holy Spirit and our sanctification.
Q25: Since there is only one divine being,  why do you speak of three: Father, Son, and Holy Spirit?
A25: Because that is how God has revealed himself in his Word:  these three distinct persons are one, true, eternal God.
 Deuteronomy 6:4 NKJV "Hear, O Israel: The LORD our God, the LORD is one!
1 Corinthians 8:4 NKJV Therefore concerning the eating of things offered to idols, we know that an idol is nothing in the world, and that there is no other God but one.
1 Corinthians 8:6 NKJV yet for us there is one God, the Father, of whom are all things, and we for Him; and one Lord Jesus Christ, through whom are all things, and through whom we live.
 Matthew 3:16-17 NKJV When He had been baptized, Jesus came up immediately from the water; and behold, the heavens were opened to Him, and He saw the Spirit of God descending like a dove and alighting upon Him. (17) And suddenly a voice came from heaven, saying, "This is My beloved Son, in whom I am well pleased."
Matthew 28:18-19 NKJV And Jesus came and spoke to them, saying, "All authority has been given to Me in heaven and on earth. (19) Go therefore and make disciples of all the nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit,
Luke 4:18 NKJV "The spirit of the Lord is upon me, because He has anointed me to preach the gospel to the poor; He has sent me to heal the brokenhearted, to proclaim liberty to the captives and recovery of sight to the blind, to set at liberty those who are oppressed;
John 14:26 NKJV But the Helper, the Holy Spirit, whom the Father will send in My name, He will teach you all things, and bring to your remembrance all things that I said to you.
John 15:26 NKJV "But when the Helper comes, whom I shall send to you from the Father, the Spirit of truth who proceeds from the Father, He will testify of Me.
2 Corinthians 13:14 NKJV The grace of the Lord Jesus Christ, and the love of God, and the communion of the Holy Spirit be with you all. Amen.
Galatians 4:6 NKJV And because you are sons, God has sent forth the Spirit of His Son into your hearts, crying out, "Abba, Father!"
Titus 3:5-6 NKJV not by works of righteousness which we have done, but according to His mercy He saved us, through the washing of regeneration and renewing of the Holy Spirit, (6) whom He poured out on us abundantly through Jesus Christ our Savior,