The Bible refers to the “foundation” of the world in various passages. To “found” something is to establish a thing or lay the groundwork or secure the underpinnings for it. The “foundation of the world” is a reference to God’s act of creation. When Scripture refers to something that has been true “from the foundation of the world,” it means “for all of human history.” But when Scripture refers to something that happened “before the foundation of the world,” it specifically refers to the time prior to the creation of the earth and more broadly, before anything was ever created, in eternity past.
In Ephesians 1, we read of something that happened in eternity past: “According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love:” Ephesians 1:4 Before God had created anything at all, at least three things were already true: God saw mankind as lost and in need of a Savior; the eternal Savior was present; and the details of the work of redemption were planned out. In all of this, God had mans transformation to holiness in view. “Who hath saved us, and called us with an holy calling, not according to our works, but according to his own purpose and grace, which was given us in Christ Jesus before the world began” 2 Timothy 1:9
“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 Christ, 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, Who by him do believe in God, that raised him up from the dead, and gave him glory; that your faith and hope might be in God.” 1 Peter 1:18-21 This passage shows God’s eternal plan involving Jesus was concieved before the world itself was created. (1 Peter 1:20) “But we speak the wisdom of God in a mystery, even the hidden wisdom, which God ordained before the world unto our glory:” 1 Corinthians 2:7
The eternal nature of God the Son and His eternal relationship with God the Father existed prior to the creation of the world: “Father, I will that they also, whom thou hast given me, be with me where I am; that they may behold my glory, which thou hast given me: for thou lovedst me before the foundation of the world.” John 17:24 The Son of God is not a created being; He possessed glory with the Father, was loved by the Father, and dwelt with the Father before the universe was created (John 1:1–2).
God’s plan of salvation, being eternal, is unchanging; nothing can frustrate, amend, or impede that plan. From before the foundation of the world, God laid out His design to love, redeem, shower with grace and make believers holy. “But when the fulness of the time was come, God sent forth his Son, made of a woman, made under the law, To redeem them that were under the law, that we might receive the adoption of sons.” Galatians 4:4–5.