Many people of other faiths will question a Christian's belief in the Trinity. They will ask us why we believe that Jesus is God. Often they aren't asking us to learn, but really just to argue with us. This past year I have dealt online with many Jehovah's Witnesses. They do not believe Jesus is God and they want to argue that point over and over and over. They are relentless on this subject. Muslims will often argue the divinity of Jesus with Christians. Sadly, most Christians don't know how to answer their questions/ address their arguments or even where to begin.
Christians believe in the Trinity. It is an essential to our faith.
In my blogs when I refer to "God" - I am thinking in my mind of God as the Father, Jesus, and the Holy Spirit. When I say "God," I am referring to the Trinity.
Our Old Testament is the same as the written Jewish Scriptures (organized differently though, but the same text.) The Jewish Scriptures were written in Hebrew (well, mostly Hebrew with a very small part written in Aramaic.) A Hebrew word frequently used to refer to God in the Jewish Scriptures is Elohim and it is a plural form. ['elohiym is the Hebrew spelling/ elohim is the English transliteration.] Plural means more than one. There is a singular form of Elohim and it is El. So why did they use the plural form?
In the New Testament the divinity of Jesus is put forth. (See John 1:1-5/ John 1:14/ John 5:18-24/ Titus 2:13/ 2 Peter 1:1)
Jesus says He can forgive sins. (Matthew 9:1-8/ Mark 2:1-12/ Luke 7:48)
Jesus says He has the right to judge mankind. (Luke 22:30/ John 5:22/ John 9:39)
Jesus performed miracles through His own authority. (Matthew 12:28/ Luke 11:20)
Jesus spoke with His own authority. (Matthew 28:18/ Mark 9:1/ Luke 23:43)
Jesus claims to be God in John 8:58 when He says "... before Abraham was born, I am." This refers to Genesis 3:14 when God told Moses His name was "I AM." The Jews understood what Jesus was claiming here because they picked up stones to stone Him. Another example where Jesus claims to be God is Mark 14:62 which refers to Psalm 110:1 and Daniel 7:13-14. Again the Jewish high priest knew exactly that Jesus was claiming to be God.
In John 20:28 where Thomas sees the resurrected Jesus and said, "My Lord and my God!" see Jesus' response to Thomas in verse 29. Does Jesus correct Thomas and say, "Whoa, you've got it wrong!" No, Jesus said to him, "Because you have seen Me, have you believed? Blessed are they who did not see, and yet believed." Jesus affirms Thomas' belief that He is his Lord and God.
[I highly recommend you spend some time looking up the referenced Scripture to see how Jesus revealed His divinity to us.]
Christians believe in the Trinity - God is three in One - the Father, the Son, and the Holy Spirit.
The Apostle John tells us that Jesus was at creation.
In the beginning was the Word, and the Word was with God, and the Word was God. He was in the beginning with God. All things came into being through Him, and apart from Him nothing came into being that has come into being.
Christianity is a monotheistic religion meaning there is only one God.
... whereas God is only one.
Judaism is also a monotheistic religion.
"Hear, O Israel! The LORD is our God, the LORD is one!"
There is abundant evidence in the Bible that God is One and that His oneness, involves three "persons."
In the beginning God created the heavens and the earth.
In the Hebrew manuscripts for Genesis 1:1, the word for "God" is Elohim. Plural. This does not mean there is gods. Elohim means there is one sovereign God - the Trinity.
Now go to Genesis 1:26:
Then God said, "Let Us make man in Our image, according to Our likeness; and let them rule over the fish of the sea and over the birds of the sky and over the cattle and over all the earth, and over every creeping thing that creeps on the earth.
See that? The pronouns are plural.
(And they are capitalized because I read from the New American Standard Bible - NASB - which capitalizes all pronouns referring to the Father, Jesus, and the Holy Spirit out of reverence and for clarity.)
Now go to Genesis 3:22:
Then the LORD God said, "Behold, the man has become like one of Us, knowing good and evil;...
See the plural?
Now got to Genesis 11:7:
"Come, let Us go down and there confuse their language, so that they will not understand one another's speech."
Again, plural "Us."
The Spirit is mentioned many times in the Old Testament, but we see Him first in Genesis 1:2. ... and the Spirit of God was moving over the surface of the waters.
The Father, Jesus, and the Holy Spirit were at creation.
The sovereign God created everything.
Elohim isn't just used once or twice in the Hebrew manuscripts.
It is used 2,346 times!
(Remember there is a singular form, El, that could have been used.)
Does that not blow you away?!
So why does this matter?
First to give an answer to those who are seeking. Know why you believe what you believe. "Apologetics" is the discipline of defending your faith. See 1 Peter 3:15. Christians should be able to explain to others the hope that is in us. We should be able to explain the foundations of our faith.
And it matters because many Christians camp out only in the New Testament. I've heard people say, "I only need to listen and obey Jesus' words." or "I only have to read the New Testament." That is just illogical.
Follow my reasoning:
Christians believe Jesus is God.
God is everlasting and unchangeable.
Jesus was at creation and throughout all time.
So when Elohim/God spoke in the Old Testament, it was Jesus speaking too.
So you can't just go along with what Jesus says in the New Testament and ignore what He says in the Old Testament.
And why would you want to? I suspect because you have this view that God in the Old Testament is angry and Jesus in the New Testament is compassionate. If you have that view, you haven't read the Old Testament because God is repeatedly described as abundant in lovingkindness for us. And yes, Jesus was compassionate. But that is because Jesus is God. Or I suspect you don't get how the Old Testament points to Christ coming to us. Maybe you don't get the connection between the two. The entire Bible - the Old Testament and New Testament - is the holy Word of God. It has a unified body of teaching to us.
God is God. He is eternal. His nature is the same at the beginning of time as it is now. He was and is and will be holy and loving. And by "He" I mean the Trinity.
Our one God is Father, Son, and Spirit.
When you are reading the Old Testament and you see the word "God" or "LORD", you should think in your mind of the Father, Son, and Holy Spirit. You should think of the Trinity. When you are reading in the New Testament, if the text says God the Father or the Father; or Jesus or Christ or Son; or Spirit; it is specifically talking about one part of the Deity. (Colossians 2:9 for example where it is talking about Jesus.)
God = Trinity = the Father, the Son, the Spirit
LORD = Trinity = the Father, the Son, the Spirit
Train your mind to think of the Trinity when reading the Bible.
Jesus Christ is the same yesterday and today and forever.
New International Version study Bible, copyright 1984
English Standard Version study Bible, copyright 2008
Living Beyond Yourself - Exploring the Fruit of the Spirit by Beth Moore, copyright 1998, revised 2004, eighteenth printing 2012, Life Way Press, page 33
So What's the Difference? by Fritz Ridenour, copyright 2001, Regal Books, page 18
James Strong, The New Strong's Concordance of the Bible [Nashville, TN; Thomas Nelson Publishers, 1984]
Blue Letter Bible website https://www.blueletterbible.org/lang/lexicon/lexicon.cfm?Strongs=H430&t=NASB
See also: Amen about Jesus speaking with authority.