How long was this on God's mind? That is, His purpose of having a sacrifice - thus enabling Him to pay for the sins of mankind? We know that sin kills. And, if a person is required to pay for his own sin, then he dies - because the wages of sin is death. [Romans 6:23] Well, God purposed (it says, long before the foundation of the world) that once sin began, the only way that it could be paid for would be through the death of either (1) the individual who sinned, or (2) a substitution who could take the place of those who sinned. But that substitution had to be sinless! And we find that this death had to be of One who was greater than all of the creation.