We have often heard how Christ was slain from the foundation of the world. I have heard many explanations concerning this but perhaps this is one of the best.
"As the divine Sufferer hung upon the cross, angels gathered about Him, and as they looked upon Him, and heard His cry, they asked, with intense emotion, "Will not the Lord Jehovah save Him?" . . . Then were the words spoken: "The Lord hath sworn, and He will not repent. Father and Son are pledged to fulfill the terms of the everlasting covenant. God so loved the world, that He gave His only-begotten Son, that whosoever believeth in Him should not perish, but have everlasting life." Christ was not alone in making His great sacrifice. It was the fulfillment of the covenant made between Him and His Father before the foundation of the world was laid. With clasped hands they had entered into the solemn pledge that Christ would become the surety for the human race if they were overcome by Satan's sophistry." FLB 76
I think about our exceeding wickedness and yet the Father and Son from the beginning knowing all this and what it would cost them both only had endless love for us. Thus They both gave all and Christ became our priest and king.
"Even he shall build the temple of the LORD; and he shall bear the glory, and shall sit and rule upon his throne; and he shall be a priest upon his throne: and the counsel of peace shall be between them both." (Zec 6:13)
I fall at Their feet and can only declare - what wondrous love that we who were once bound to sin and death should be called sons and daughters of the Most High. Words fail me!