The 'forgotten' Trinity verses.

All too often, defending the Trinity from the Bible comes down to merely looking to a few verses that show the divinity of Jesus or the Holy Spirit. This is the approach many apologetics sources today take. But this approach leaves out an equally important and traditional approach, which is to look to the texts which speak of all three Persons within the same breath. What is important to keep in mind when reading these texts is to see them as the early Christians, especially Jewish Christians saw them, namely by recognizing the simple fact that no created thing can or should be mentioned alongside God, since this implied the blasphemy of making created things equal to Him. Another thing to keep in mind is that when the term "God" is used in the Bible, it quite often refers to the Father specifically, and as a way to distinguish between the Son and Holy Spirit. There are other passages that mention the Trinity which are good to know about, but here are some of the more prominent ones:

• Matthew 3:16 After being baptized, Jesus came up immediately from the water; and behold, the heavens were opened, and he saw the Spirit of God [the Father] descending as a dove and lighting on Him, 17 and behold, a voice from heaven said, “This is my beloved Son, with whom I am well pleased.”
  
  
• Matthew 12:28 But if I [Jesus] cast out demons by the Spirit of God [the Father], then the kingdom of God has come upon you.
  
  
• Matthew 28:19 Go therefore and make disciples of all the nations, baptizing them in the name of the Father and the Son and the Holy Spirit . . .
  
  
• Luke 3:22 And the Holy Spirit descended upon Him [Jesus] in bodily form like a dove, and a voice came out of heaven, “You are My [the Father’s] beloved Son, in You I am well-pleased.”
  
  
• John 14:26 But the Helper, the Holy Spirit, whom the Father will send in My [Jesus’] name, He will teach you all things, and bring to your remembrance all that I said to you.”
  
  
• John 15:26 When the Helper comes, whom I [Jesus] will send to you from the Father, that is the Spirit of truth who proceeds from the Father, He will testify about Me . . .
  
  
• Acts 1:4 Gathering them together, He [Jesus] commanded them not to leave Jerusalem, but to wait for what the Father had promised, “Which,” He said, “you heard of from Me 5 for John baptized with water, but you will be baptized with the Holy Spirit not many days from now.”
  
  
• Acts 2:33 Therefore having been exalted to the right hand of God [the Father], and having received from the Father the promise of the Holy Spirit, He [Jesus] has poured forth this which you both see and hear.
  
  
• Acts 10:38 You know of Jesus of Nazareth, how God [the Father] anointed Him with the Holy Spirit and with power, and how He went about doing good and healing all who were oppressed by the devil, for God was with Him.
  
  
• Romans 1:4 Who was declared the Son of God [the Father] with power by the resurrection from the dead, according to the Spirit of holiness, Jesus Christ our Lord . . .
  
  
• Romans 14:17 For the kingdom of God [the Father] is not a matter of eating and drinking but of righteousness and peace and joy in the Holy Spirit. 18 Whoever thus serves Christ is acceptable to God and approved by men.
  
  
• Romans 8:9 However, you are not in the flesh but in the Spirit, if indeed the Spirit of God [the Father] dwells in you. But if anyone does not have the Spirit of Christ, he does not belong to Him.
  
  
• 1 Corinthians 6:11 Such were some of you; but you were washed, but you were sanctified, but you were justified in the name of the Lord Jesus Christ and in the Spirit of our God [the Father].
  
  
• 1 Corinthians 12:4 Now there are varieties of gifts, but the same Spirit; 5 and there are varieties of service, but the same Lord [Jesus]; 6 and there are varieties of activities, but it is the same God [the Father] who empowers them all in everyone.
  
  
• 2 Corinthians 1:21 And it is God [the Father] who establishes us with you in Christ, and has anointed us, 22 and who has also put his seal on us and given us his Spirit in our hearts as a guarantee.
  
  
• 2 Corinthians 13:14 The grace of the Lord Jesus Christ, and the love of God [the Father], and the fellowship of the Holy Spirit, be with you all.
  
  
• Galatians 4:6 Because you are sons, God [the Father] has sent forth the Spirit of His Son into our hearts, crying, “Abba! Father!”
  
  
  
• Ephesians 2:18 For through Him [Jesus] we both have our access in one Spirit to the Father.
  
  
• Ephesians 2:22 In whom [Jesus] you also are being built together into a dwelling of God [the Father] in the Spirit.
  
  
• Ephesians 4:4 There is one body and one Spirit—just as you were called to the one hope that belongs to your call— 5 one Lord [Jesus], one faith, one baptism, 6 one God and Father of all, who is over all and through all and in all.
  
  
• Hebrews 9:14 How much more will the blood of Christ, who through the eternal Spirit offered Himself without blemish to God [the Father], cleanse your conscience from dead works to serve the living God?
  
  
• 1 Peter 1:2 According to the foreknowledge of God the Father, by the sanctifying work of the Spirit, to obey Jesus Christ and be sprinkled with His blood: may grace and peace be yours in the fullest measure.
  
  
• Jude 20 But you, beloved, building yourselves up in your most holy faith and praying in the Holy Spirit, 21 keep yourselves in the love of God [the Father], waiting for the mercy of our Lord Jesus Christ that leads to eternal life. 

I didn't come up with this list myself, but rather freely referenced a few good existing resources from elsewhere, such as HERE and HERE. I knew about many of these passages, but am thankful to learn about the others.