Yahuwshuwa HaMashiyach (Jesus Christ) is called the Word because he is the Messenger of His Father, the Mediator between the Father and Man, fulfilling His Father's will in all things.
John 12:49 For I have not spoken of myself; but the Father which sent
me, he gave me a commandment, what I should say, and what I should
speak.
He is the Word because he is the manifestation of the Fathers divine word and will.
John 14:9 Jesus saith unto him, Have I been so long time with you, and
yet hast thou not known me, Philip? he that hath seen me hath seen the
Father; and how sayest thou then, Shew us the Father?
"The Word" is not just a New Testament thing, we can take a journey throughout the scriptures and see The Word moving among the Patriarchs and prophets of old, we can even see the Word in creation.
The Father did all things through the Word. He revealed Himself and communicated to the prophets through the Word:
1 Samuel 3:7 Now Samuel did not yet know the LORD, neither was the
word of the LORD yet revealed unto him.
1 Samuel 3:21
And the LORD appeared again in Shiloh: for the LORD revealed himself to Samuel in
Shiloh by the word of the LORD.
Genesis 15:1 After these things the word of the LORD came unto Abram in a vision, saying, Fear not, Abram:
I am thy shield, and thy exceeding great reward.
Jeremiah 1:4-5 Then the word of the Lord came unto me, saying, Before I formed thee in the
belly I knew thee; and before thou camest forth out of the womb I
sanctified thee, and I ordained thee a prophet unto the nations.
These were actual appearances of the Son delivering His Father's divine words to man. This is why he called the Word. The Father always revealed Himself through His Son. In Genesis 15:1 it showed that Abraham seen the Word in the vision. many who read these passages might think these were just spoken words of the Father, but no it was actually the Son who's name is the Word:
Revelation 19;13 And he was clothed with a vesture dipped in blood:
and his name is called The Word of God.
But now lets start from the beginning:
genesis 1:1 In the beginning God created the heaven and the earth.
The scriptures specifically shows us how all things were created:
Psalm 33:6 By the word of the LORD were the heavens made; and all
the host of them by the breath of his mouth.
Its likely This is where the Apostle John made the connection with the Word being in the beginning with God, and that all things were made by him. And he identified this Word as the Son, he says this word took on flesh and dwelled among us.:
John 1:1-3 In the beginning was the Word, and the Word was with God,
and the Word was God. The same was in the beginning with God. All
things were made by him; and without him was not any thing made that
was made.
The Apostle Paul also made these connections, except he interchanged "The Word" with "Jesus Christ", showing that This Word was indeed the Son that took on flesh:
Ephesians 3:9 And to make all men see what is the fellowship of the
mystery, which from the beginning of the world hath been hid in God,
who created all things by Jesus Christ:
Colossians 1:14-16 In whom we have redemption through his blood, even
the forgiveness of sins: Who is the image of the invisible God, the
firstborn of every creature: For by him were all things created
1 Corinthians 8:6(KJV) But to us there is but one God, the Father, of
whom are all things, and we in him; and one Lord Jesus Christ, by whom
are all things, and we by him.
That word BY literally means THROUGH, so its saying all things were created THROUGH the Son. The author of Hebrews even explains how this was done:
Hebrew 1:2 Hath in these last days spoken unto us by his Son, whom he
hath appointed heir of all things, by whom also he made the worlds;
So the author illustrates for us how this was done. the same exact way the Father spoke through his Son during His earthly ministry, being inside His Son, is the same way he created the words THROUGH his Son the Word.
compare it to acts 2:22
Ye men of Israel, hear these words; Jesus of Nazareth, a man approved
of God among you by miracles and wonders and signs, which God did by
him in the midst of you, as ye yourselves also know:
Again, same way God did miracles through His Son, is the same way He created all things. The Word was with the Father is the beginning , as John explained. This is why there was more than one in the beginning when the Most High said in genesis 1:26
And God said, Let us make man in our image, after our
likeness: and let them have dominion over the fish of the sea, and
over the fowl of the air, and over the cattle, and over all the earth,
and over every creeping thing that creepeth upon the earth.
Some might think this contradicts isaiah 44:24
Thus saith the LORD, thy redeemer, and he that formed thee from the
womb, I am the LORD that maketh all things; that stretcheth forth
the heavens alone; that spreadeth abroad the earth by myself;
but it does not contradict. Right here the Father is showing His preeminence above all. The prophets and apostles never said the Father and Son created together helping eachother, they said THE FATHER CREATED ALL THINGS, and he created them THROUGH his Son. The Son said he could do nothing of his own ( John 5:19-20), and that he learned all things from His Father, and that His Father is greater than Him. So this does not contradict.
we can see that the Word was also prophesied to be exalted :
Psalm 138:2 I will worship toward thy holy temple, and praise thy name
for thy lovingkindness and for thy truth: for thou hast magnified
thy word above all thy name.
which was fulfilled through Yahuwshuwa HaMashiyach:
Ephesians 1:20-22 Which he wrought in Christ, when he raised him from
the dead, and set him at his own right hand in the heavenly places,
Far above all principality, and power, and might, and dominion, and
every name that is named, not only in this world, but also in that
which is to come: And hath put all things under his feet, and gave him
to be the head over all things to the church,
and we also see it was shown from the old testament that The Word would be sent to save us from our sins and heal us by his stripes:
Pslams 107
17 Fools because of their transgression, and because of
their iniquities, are afflicted.
18 Their soul abhorreth all manner of meat; and they draw near unto
the gates of death.
19 Then they cry unto the Lord in their trouble, and he saveth them
out of their distresses.
20 He sent his word, and healed them, and delivered them from their
destructions.
How would he heal us?
Isaiah 53:5. But He was wounded because of our transgressions; He was
crushed because of our iniquities; The chastening for our peace was
upon Him, And by His stripes we have been healed.
So in this answer i wanted to show you why he is called the Word, but also i wanted to show you the Word can be found all through the scriptures.