There are many reasons; however, for us humans the most important is that without God paying the price for our sins (in the person of Christ), God could not be just and yet also be the Justifier of the unjust (as St Paul declares Him to be in Rom. 3:21-25).
Without this Just dying for the unjust, God’s justice would not be satisfied, and without justice being appeased God’s mercy could not be released to declare the otherwise unjust sinners to be justified in His eyes and, hence, qualified for heaven.
I agree with you.