The Trinity is one of the foundation doctrines of Christianity, and it is also a particularly important when it comes to apologetics. First, we’re going to establish what the Trinity is, then explain the Scriptural backing for the doctrine, and ultimately show how it is useful for apologetics.
For the purposes of our discussion, we need to show from Scripture two aspects of the Trinity. We need to show that the Father, the Son, and the Holy Spirit are all God, yet we need to also show that they are not the same person, while being the same being.
There is a heavy emphasis in the Old Testament on the oneness of God, and so it’s helpful to start there. In Deuteronomy 6:4 we read “Hear, O Israel: The Lord our God, the Lord is one.”
Also, there are several statements where God writes to His people about the fact that there are no other gods (Deut. 32:39, 4:9; 2 Kings 19:15; Neh. 9:6; Mal. 2:10 etc.) , which support the fact that there is only one God (while also serving as a helpful starting place for discussing Polytheism/Pantheism).
The New Testament does restate some of the truths mentioned in the Old Testament about the unity of God (1 Cor. 8:4; John 17:3), what it emphasizes more is the distinction between the persons of the Godhead, while at the same time affirming their divinity.
The fact the the Father is God is something that is usually noncontroversial, even among other belief systems. So I won’t touch on that aspect apart from showing the unity in that all three are God in a later section. Instead, I’m going to focus on how we know that the Spirit and the Son are God.
There are a number of ways to go about showing that Jesus is God. One way is to show that Jesus is the Christ, the Messiah, and that He fulfilled quite a large number of Old Testament prophecies.
Having established this, then you can begin to make certain connections. For example, you can read in Psalm 45:6, a description of God that is then quoted in Hebrews 1:8 as being applied to Jesus. Or you could make the connection between Isaiah 7:14 and Matthew 1:23, which identifies Jesus as Immanuel – God with us. Alternatively, you can point to the opening of John’s gospel, which says that “In the beginning was the Word, and the Word was with God, and the Word was God.” and continue all through the first chapter of John, where we see John continuing to write about Jesus in some of the most wonderful texts of Scripture, all the way through the recounting of John the Baptist identifying Jesus as the Lamb of God. Of particular note in the first chapter as well, is 1:18, which clearly identifies Jesus as God, while at the same time makes clear the distinction of the persons of the Father and the Son.
In John 20:28, we have Thomas referring to Jesus as both Lord and God. In Acts 20:28, we have Paul writing to the Ephesians, and exhorting the elders of the church to “Pay careful attention to yourselves and to all the flock, in which the Holy Spirit has made you overseers, to care for the church of God, which he obtained with his own blood.” which makes the clear connection that Jesus is God. In Romans 9:5, Paul straight forwardly calls Jesus “God over all, blessed forever.” In Titus 2:13, Paul does it again, when he calls Jesus “our God and Savior.” This is a pair of titles that Peter repeats in 2 Peter 1:1.
There is also another especially powerful verse in which Jesus calls Himself God. In John 8:58, He says “Truly, truly, I say to you, before Abraham was, I am.” He not only speaks of His preexistence, but also identifies Himself with the special name of God, I am. The Jews he was interacting with immediately knew what that meant, as they instantly started looking for stones, to stone Him for blasphemy.
In a similar way, connecting the Old & New testaments, it can also be shown that the Holy Spirit is identified as God. There are connections made between Jeremiah 31:33-34 and Hebrews 10:15-17, as well as Psalm 95:7-11 and Hebrews 3:7-11, to name a couple.
The Scriptures also list the Spirit as having divine attributes. He is eternal (Heb. 9:14), omniscient (Isa. 40:13; 1 Cor. 2:10-11), omnipresent (Ps. 139:7-10; Acts 1:8), and obviously is called holy.
While it is true that the word “Trinity” does not appear in the Bible (neither does the word Bible), the understanding behind what the word means is all over the place. There are a number of places throughout the Bible that list the three persons together: Matt. 28:19; Rom. 15:19; 2 Cor. 13:14; Rev. 1:4-5. Also, while the Old Testament doesn’t refer to the three persons in the same terms, there are places we can tell that while God is definitely one, there is also plurality in Him (that is, multiple persons). Particularly in Genesis, God refers to Himself in the plural (1:26, 3:22, 11:6).
The reason for going through this brief overview is that it’s easier, in my opinion, to show the Trinity from the Bible than it is to try and explain what the Trinity is. While it is tempting to use an analogy, you don’t want to end up like St. Patrick.
While it may take significantly more time to take people through the Scriptures to show where and why we believe the Trinity, it does them a greater service, because all attempts at analogies end up not teaching the totality of the truth. In order to help people understand the Trinity, I have often used a simple diagram like this one to help illustrate the basic idea.
However, ultimately, you always want to get back to the Scriptures. Familiarizing yourself with just a few of these passages will help you when you are talking with people of different religions, especially Mormonism, Jehovah’s Witnesses, and Muslims. The reason for this is that all three of these religions deny the Trinity. Particularly, they will deny that Jesus is God. In Islam, Jesus is merely a prophet of Allah. In Jehovah’s Witness belief, Jesus is actually Michael the Archangel. In Mormonism, Jesus is a god, and while they are comfortable in equating Him with Jehovah in the Old Testament, they would not say that He is Elohim (their name for God the Father).
While I’m sure we will get to each of these different religions in their own post, I want to make a quick mention on tactics. If you are talking to a Jehovah’s Witness, and you try to go to John 1:1 as a proof of the divinity of Christ, you will be tripped up by the fact that their translation (New World Translation) inserts the article “a” so that the Word was a God. Instead, what you should do is go back to the Psalm 45:6 & Hebrews 1:8 connection. The reason for this is that they will gladly admit that the Psalms passage is referring only to Jehovah (their name for God the Father) and the passage in Hebrews can only refer to God the Son. However, in the notes in their own translation, the Hebrews passage will be linked back to the Psalms passage.
Interestingly, you can use this same connection with a Mormon as well. The reason for this is because the word used to translate “God” in the Psalms passage is Elohim. As Christians, we know that Jehovah and Elohim are actually our terms that the people of these different religions are using, so we certainly aren’t afraid of them, and they are all referring to the glorious truth of the divinity of Christ! It’s a powerful testament to the truth of the Christian worldview. Hopefully this will help you out in your understanding of this foundational doctrine, and how to apply it in apologetics conversations.