"Foreordained" means to foreknow. YHWH knew He would create Yeshua long before he came into existence just as He "chose" and "predestined" believers we existed.
Eph 1:4 According as He has chosen us in him before the foundation of the world, that we should be holy and without blame before Him in love:
Eph 1:5 Having predestinated us unto the adoption of children by Yeshua Messiah to Himself, according to the good pleasure of His will,
Yeshua is said to be the Lamb which was slain from the foundation of the world (Revelation 13:8), yet we have the Bible also saying, "Nor yet that he should offer himself often, as the high priest entereth into the holy place every year with blood of others; For then must he often have suffered since the foundation of the world: but now once in the end of the world hath he appeared to put away sin by the sacrifice of himself." (Hebrews 9:25-26)
Clearly, the Hebrews passage states that Yeshua was not literally slain from the foundation of the world, but rather was slain in the mind or plan of Almighty YHWH. This is akin to John 1:1 which speaks of the very word of Elohim being with Elohim in the beginning. This spoken word or plan of YHWH existed throughout the ions of time. From the beginning of time, YHWH had Yeshua's sacrifice in His plan for all humankind. For it was through Yeshua that we would receive our justification (Romans 4:25). 1 Peter 1:18-20 continues to explain this by saying:
"Forasmuch as ye know that ye were not redeemed with corruptible things, as silver and gold, from your vain conversation received by tradition from your fathers; But with the precious blood of Messiah, as of a lamb without blemish and without spot: Who verily was foreordained before the foundation of the world, but was manifest in these last times for you."
Yeshua was foreordained (foreknown) from the foundation of the world, but was made manifest or revealed in these last times. He did not exist as a person or being in former times, but in these last times YHWH allowed him to be born of a woman (Galatians 4:4) and speaks through him (Hebrews 1:1-2).
The glory that Yeshua had was as the slain lamb of YHWH, in the mind of YHWH, and Yeshua was praying for that glory to be brought about literally, so as to give unto all those who would accept, eternal life. This is why Yeshua began in John 17:1-2 by saying, 'Father, the hour is come; glorify thy Son, that thy Son also may glorify thee: As thou hast given him power over all flesh, that he should give eternal life to as many as thou hast given him.' " Yeshua wanted to bring about the fulfillment of the plan of salvation by YHWH glorifying him as the ultimate sacrifice, and Yeshua in turn glorifying the Father.
Paul was addressing two separate issues; 1) Yeshua being the image of the invisible God and 2) Yeshua being the firstborn of every creature.
1) If it was possible to see the invisible God, He would look like Yeshua, not outwardly, but inwardly via his character, dedication, faith, obedience, love, etc.
2) Of all the creatures that YHWH created, Yeshua was the "firstborn" or first to be "begotten again" via a resurrection unto eternal life.
Also, Paul says Yeshua is the "image" of the invisible God. He did NOT say Yeshua IS the invisible God. An image is a replica of the original. A painting of an apple is not an apple. Neither is an image of the only true God, the only true God.