@Rattigan350
Here is what Barnes has to say
1 Peter 1:20
Who verily was foreordained before the foundation of the world - That is, it was foreordained, or predetermined, that he should be the great stoning Sacrifice for sin. On the meaning of the word “foreordained,” (προγινώσκω proginōskō,) see Rom_8:29. The word is rendered which knew, Act_26:5; foreknew and foreknow, Rom_8:29; Rom_11:2; foreordained, 1Pe_1:20; and know before, 2Pe_2:17. It does not elsewhere occur in the New Testament. The sense is, that the plan was formed, and the arrangements made for the atonement, before the world was created.
Before the foundation of the world - That is, from eternity. It was before man was formed; before the earth was made; before any of the material universe was brought into being; before the angels were created. Compare the Mat_25:34 note; Joh_17:24 note; Eph_1:4 note.
But was manifest - Was revealed. See the notes at 1Ti_3:16.
In these last times - In this, the last dispensation of things on the earth. See the notes at Heb_1:2.
For you - For your benefit or advantage. See the notes at 1Pe_1:12. It follows from what is said in this verse:
(1) That the atonement was not an afterthought on the part of God. It entered into his plan when he made the world, and was revolved in his purposes from eternity.
(2) It was not a device to supply a defect in the system; that is, it was not adopted because the system did not work well, or because God had been disappointed. It was arranged before man was created, and when none but God could know whether he would stand or fall.
(3) The creation of the earth must have had some reference to this plan of redemption, and that plan must have been regarded as in itself so glorious, and so desirable, that it was deemed best to bring the world into existence that the plan might be developed, though it would involve the certainty that the race would fall, and that many would perish. It was, on the whole, more wise and benevolent that the race should be created with a certainty that they would apostatize, than it would be that the race should not he created, and the plan of salvation be unknown to distant worlds. See the notes at 1Pe_1:12.
JFB commentary says
1 Peter 1:20
God’s eternal foreordination of Christ’s redeeming sacrifice, and completion of it in these last times for us, are an additional obligation on us to our maintaining a holy walk, considering how great things have been thus done for us. Peter’s language in the history corresponds with this here: an undesigned coincidence and mark of genuineness. Redemption was no afterthought, or remedy of an unforeseen evil, devised at the time of its arising. God’s foreordaining of the Redeemer refutes the slander that, on the Christian theory, there is a period of four thousand years of nothing but an incensed God. God chose us in Christ before the foundation of the world (Eph_1:4).