Untold eons ago, God the Father, God the Son and God the Holy Spirit,
in Their Omniscient foreknowledge, determined that mankind's Redeemer
would be a Substitute Sacrifice and a Vicarious Atonement to pay a bill 
He didn't owe, for a debt that mankind would not and could not pay.

The Message of the Cross is foolishness to those who will not hear, but to
those who are being Saved it is the single most important event in human
history.  God's Purpose:  Reconciliation between Himself and mankind.

Jesus Christ is the Lamb slain before the foundation of the Earth.

1 Peter 1 KJV

19  But with the precious blood of Christ, as of a Lamb
without blemish and without spot:
20  Who verily was foreordained before the foundation of the world,
but was manifest in these last times for you,
21  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.