The Crucifixion was a Crime: In an age of performative cruelty, we can't see Roman brutality as salvific

[TomSlick]

2. Substitutionary atonement is a difficult concept but is scripturally inescapable.

I find it difficult to understand why God would establish a system in which it was essential for his Son to die in order to secure the salvation of humanity.

The passage you cite, that Jesus is "the Lamb slain from the foundation of the world.” (Revelation 13:8) means that Jesus being killed was the plan from before the beginning.

The proclamation of the early Church was "For I handed on to you as of first importance what I in turn had received: that Christ died for our sins in accordance with the scriptures, and that he was buried, and that he was raised on the third day in accordance with the scriptures." 1 Corinthians 15:3-4

That Jesus died to expiate our sins has been a stumbling block for many since the earliest days of the Church. "But we preach Christ crucified, unto the Jews a stumbling block, and unto the Greeks foolishness...." 1 Corinthians 23 However, to reject that core belief is to reject what has always been a fundamental tenant of Christianity.