What does it mean that the Word was God and the Word was with God? John 1:1-18 NASB

First, see the big picture:

Christ in John 1

  1 Christ the Word  John 1:1

  2 Christ the Light   John 1:8

  3 Christ the Lamb of God  John 1:29,36

  4 Christ the Son of God  John 1:34,49

  5 Christ the Anointed (Messias)  John 1:41

  6 Christ the King of Israel  John 1:49

  7 Christ the Son of man  John 1:51

The Word

  1 His Eternity—in the beginning  John 1:1

  2 His Equality—was with God  John 1:1

  3 His Deity—was God  John 1:1

  4 His Humanity—was made flesh  John 1:14

  5 His Testimony—‘told the Father out’ (Margin)  John 1:18

                                               H.K.D.

Jesus Is God – John 1:1

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NET ©	In the beginning 1  was the Word, and the Word was with God, 2  and the Word was fully God. 3

The Bible teaches that Jesus is not merely someone who is a lot like God, or someone who has a very close walk with God. Rather, Jesus is the Most High God himself. Titus 2:13 says that as Christians we are “looking for the blessed hope and the appearing of the glory of our great God and Savior, Christ Jesus.” Upon seeing the resurrected Christ, Thomas cried out, “My Lord and my God!” (John 20:28). Likewise, the book of Hebrews gives us God the Father’s direct testimony about Christ: “But of the Son he says, ‘Your throne, O God, is forever and ever" and the gospel of John calls Jesus “the only begotten God” (John 1:18).

Another way the Bible teaches that Jesus is God is by showing that he has all of the attributes of God. He knows everything (Matthew 16:21; Luke 11:17; John 4:29), is everywhere (Matthew 18:20; 28:20; Acts 18:10), has all power (Matthew 8:26–27; 28:18; John 11:38–44; Luke 7:14–15; Revelation 1:8), depends on nothing outside of himself for life (John 1:4; 14:6; 8:58), rules over everything (Matthew 28:18; Revelation 1:5; 19:16;), never began to exist and never will cease to exist (John 1:1; 8:58), and is our Creator (Colossians 1:16). In other words, everything that God is, Jesus is. For Jesus is God.

From <https://www.desiringgod.org/articles/how-can-jesus-be-god-and-man#jesus-is-god>

And the Word was God (kai qeo hn o logo). By exact and careful language John denied Sabellianism by not saying o qeo hn o logo. That would mean that all of God was expressed in o logo and the terms would be interchangeable, each having the article. The subject is made plain by the article (o logo) and the predicate without it (qeo) just as in John 4:24 pneuma o qeo can only mean "God is spirit," not "spirit is God." So in 1 John 4:16 o qeo agaph estin can only mean "God is love," not "love is God" as a so-called Christian scientist would confusedly say. For the article with the predicate see Robertson, Grammar_, pp. 767f. So in John 1:14 o Logo sarx egeneto, "the Word became flesh," not "the flesh became Word." Luther argues that here John disposes of Arianism also because the Logos was eternally God, fellowship of Father and Son, what Origen called the Eternal Generation of the Son (each necessary to the other). Thus in the Trinity we see personal fellowship on an equality.

From <https://www.biblestudytools.com/commentaries/robertsons-word-pictures/john/john-1-1.html>
The Word (John 1:1–3, 14) Much as our words reveal to others our hearts and minds, so Jesus Christ is Gods Word to reveal His heart and mind to us. “He that hath seen me hath seen the Father” (John 14:9). A word is composed of letters, and Jesus Christ is Alpha and Omega” (Rev. 1:11), the first and last letters of the Greek alphabet. According to Hebrews 1:1–3, Jesus Christ is God’s last Word to mankind, for He is the climax of divine revelation.

Jesus Christ is the eternal Word (vv. 1–2). He existed in the beginning, not because He had a beginning as a creature, but because He is eternal. He is God and He was with God. “Before Abraham was, I am” (John 8:58).  -- WWW