The movie endeavors to show the historical events "as they went down," without any editorial comment or innuendo, and especially without judgmentalism. It is not about blame and finger pointing, but love and redemption. It does not convey a message of selective condemnation, but universal hope. After all, as sinners, we are all culpable in Christ's death, as Gibson points out, careful to confess his own responsibility.
I believe one of Mel Gibson's main purposes is to use the medium he knows best to spread the Gospel message, which is essentially one of love and eternal life. And the way Gibson has decided to share that message is to focus on the price Christ paid to redeem mankind.
We are so removed from Christ's suffering that we could, if not careful, view the Gospel as a mere mathematical equation. The sacrificial death of the sinless, God-incarnate cancels out the past, present and future sins of all those who place their faith in Him. But this is real life, not an abstract exercise.
God didn't just zap out man's sinfulness by divine edict. Being a God of perfect justice and unlimited mercy, He had to deal with sin -- that is, physically and spiritually deal with it. The Son, while still 100 percent God, humbled and demeaned Himself to become man, to suffer all the indignities of human existence, to become separated from the Father with whom He was united in perfect love and harmony, and to suffer His full wrath for the sum of all mankind's sins.
We must understand that for this equation to work, for man's redemption to be possible, Christ's suffering, His anxiety, His despair, His sense of betrayal and His separation from the Father had to actually occur in the flesh. "The Passion" emphasizes the reality of Christ's substitutionary suffering in the flesh. In terms that words alone cannot articulate, "The Passion" homes in on the full value of the ransom Christ paid for all of us in the greatest demonstration and act of love ever exhibited.