A very brief Biblical exposition and exegesis for the doctrine of the Trinity and the Deity and Incarnation of Christ.
Firstly a definition for of "Trinity" is due. I will supply one*: 1. There is One God. 2. There are three Persons, All of Whom possess Deity. 3. There is One only and true God, but in the unity of the Godhead there exists three eternal and co-equal Persons, the same in substance, but distinct in subsistence. These three Persons of course are known as the Father, the Son, and the Holy Spirit. Admittedly, this idea is impossible to understand completely.
Here are just a couple examples from the Old Testament that support the doctrine of the Trinity. Way back in the creation account of Genesis, the first name given for God (Genesis 1:1) is Elohim in the orininal Hebrew, a plural noun that is singular in meaning. Also in Genesis, 1:26, God says, "Let us make man in our image (emphasis mine)..."
In the New Testament there are several examples of the Trinity. Primarily, in three of the four Gospels (Matthew, Mark, and Luke) all three Persons of the Trinity can be seen simultaneously in one place- at Jesus' baptism. Matthew 3:16-17, "And Jesus (the Son), when he was baptized, went up straightway out of the water; and, lo, the heavens were opened unto him, and he saw the Spirit of God (the Holy Spirit) descending like a dove, and lighting upon him. And, lo, a voice from heaven (the Father), saying, This is my beloved Son, in whom I am well pleased." (See also Mark 1:9-11; and Luke 3:21-22)
Lastly, let's look at the Gospel of John 1:1-3, "In the beginning was the Word, and the Word was with God, and the Word was God. (2)The same was in the beginning with God. (3)All things were made by him; and without him was not anything made that was made." Here we see that the "Word" is at least in a way separate from God ("the Word was with God"), and yet at the same time, somehow "the Word was God." Also notice that the Word did all the creating, and the Word was not Himself created (verse 3). Now "the Word" is Jesus Christ. How do I know that? Look at John 1:14, "And the Word was made flesh, and dwelt among us (and we beheld his glory, the glory as of the only begotten of the Father), full of grace and truth."
Let's look again at John 1:1 "the Word was God." Because in the original Greek manuscript, "God" here lacks a definite artical, some groups (particularly the Jehova's Witnesses) have translated this to say "the Word was a god." This would be acceptible if it were not for the fact that the particular construction (θεός ήν ό λογός) is an anarthrous preverbal predicate nominative (the predicate nominative occurs before the verb and lacks a definite article). According to Colwell's Rule, such constructions have the quality of the subject in mind, rather than the subject's identity. Basically, this means that the Word possesses the same quality/characteristic of God, but is not necessarily to be identified as the same Person as God. Because of this I believe the doctrine of the Trinity is indeed Scriptural. The grammar succintly refutes Sabellianism ("the Word was the God") and Arianism ("the Word was a god"). "Jesus Christ is God and has all the attributes that the Father has. But he is not the first person of the Trinity. All this is concisely affirmed in καί θεός ήν ό λογός."**
What is the point of all this? The point is that the second Person of the Trinity, Jesus Christ- eternal God- became a man and died on the cross for your sins. I John 4:9-10, "In this was manifested the love of God toward us, that God sent his only begotten Son into the world, that we might live through him. Herein is love, not that we loved God, but that he loved us, and sent his Son to be the propitiation for our sins." How can you have a relationship with God and life through Him? John 3:16, "For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life." And finally John 1:12, "But as many as received him, to them he gave power to become the children of God, even to them that believe on his name."
* borrowed from Mr. David Glock, EBC.
**Mounce, William. Basics of Biblical Greek. Pages 27-28.