Jesus Christ had glory with the Father before the world was in the same way he was "slain from the foundation of the world" (Rev 13:8): in God's plan.
I'm sorry, but that's the wrong answer.
Hebrews 2
6But one in a certain place testified, saying, What is man, that thou art mindful of him? or the son of man, that thou visitest him?
7Thou madest him a little lower than the angels;
thou crownedst him with glory and honour, and didst set him over the works of thy hands:
8Thou hast put all things in subjection under his feet. For in that he put all in subjection under him, he left nothing
that is not put under him. But now we see not yet all things put under him.
9But we see Jesus, who was made a little lower than the angels for the suffering of death, crowned with glory and honour; that he by the grace of God should taste death for every man.
Here, the author was quoting what David, the "one" of verse 6, said in a certain place, or in Psalm 8, in relation to Jesus Christ. Before I expound a bit on what he said here, let me first establish that Jesus Christ is both God and the Creator of all things. Here are but a couple of many possible examples that I could easily give of this biblical truth:
John 1
1In the beginning was the Word, and the Word was with God, and
the Word was God.
2The same was in the beginning with God.
3All things were made by him; and without him was not any thing made that was made.
Colossians 1
16For by him were all things created, that are in heaven, and that are in earth, visible and invisible, whether they be thrones, or dominions, or principalities, or powers: all things were created by him, and for him: 17And he is before all things, and by him all things consist.
18And he is the head of the body, the church: who is the beginning, the firstborn from the dead; that in all
things he might have the preeminence.
Jesus is God (John 1:1). He was there in the beginning (John 1:1), or he is before all things (Colossians 1:17). By him all things consist (Colossians 1:17), or all things were made by him, and without him was not anything made that was made (John 1:3). The all things that he made or created includes things that are in heaven (Colossians 1:16), or things which are normally invisible (Colossians 1:16), such as angelic beings, which are here described as thrones, dominions, principalities, or powers (Colossians 1:16).
Although Jesus made or created the angels as God, there was a time, during his incarnation, when he was made a little lower than the angels for the suffering of death (Hebrews 2:9), even as had been foretold in Psalm 8:5. After his resurrection from the dead and ascension back to the Father in heaven, Jesus was crowned with glory and honor (Psalm 8:5, Hebrews 2:9). In other words, this is when Jesus' prayer request in John 17:5 was fulfilled, or this is when the Father glorified Jesus with the glory that he had with him before the world was.
The major difference, however, is that now Jesus was restored to his former glory as
both God and man. Again, it is only because Jesus has been restored to his former glory as a man, or in his humanity, that we can share in his glory as human beings ourselves (John 17:22).
With these truths in mind, let's take a quick look at what Paul wrote to the saints at Philippi.
Philippians 2
5Let this mind be in you, which was also in Christ Jesus:
6Who, being in the form of God, thought it not robbery to be equal with God: 7But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men:
8And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross.
9Wherefore God also hath highly exalted him, and given him a name which is above every name:
10That at the name of Jesus every knee should bow, of
things in heaven, and
things in earth, and
things under the earth;
11And
that every tongue should confess that Jesus Christ
is Lord, to the glory of God the Father.
It's the same exact scenario as the one that I've been describing all along.
Before his incarnation, or before he made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men (Philippians 2:7), Jesus was in the form of God, and he had equality with God (Philippians 2:6). During his incarnation, he was made a little lower than the angels for the suffering of death (Psalm 8:5, Hebrews 2:9). or he became obedient unto death, even the death of the cross (Philippians 2:8). After his resurrection from the dead and ascension back to the Father in heaven, God the Father highly exalted him, and gave him a name which is above every name (Philippians 2:9), or crowned him with glory and honor (Psalm 8:5, Hebrews 2:9), that at the name of Jesus every knee should bow, of things in heaven, and things in the earth, and things under the earth, and that every tongue should confess that Jesus Christ is Lord, to the glory of God the Father (Philippians 2:10-11). This last part is very important in relation to this present discussion because it is a fulfillment of what the prophet Isaiah wrote here:
Isaiah 45
22Look unto me, and be ye saved, all the ends of the earth:
for I am God, and there is none else.
23I have sworn by myself, the word is gone out of my mouth in righteousness, and shall not return, That unto me every knee shall bow, every tongue shall swear.
GOD spoke this, and this
GOD who spoke it was none other than Jesus Christ.
JESUS is the
GOD who swore this by himself, and what he swore is that unto him every knee shall bow, and every tongue shall swear or confess, even as Paul rightly attributed this to him in his epistle to the Philippians.
JESUS CHRIST IS GOD.
To deny this truth is to deny him.
I'd strongly advise you and anybody else reading this who presently believes otherwise to repent and to adjust your beliefs in accordance to what the Bible actually teaches in relation to who Jesus Christ truly is.