Unless Christians fully understand the ABSOLUTE holiness and righteousness of God (which includes His perfect justice) they will never understand why our holy God demanded the just retribution, punishment, and penalty for sin.
1. SIN IS OPPOSITION TO THE HOLY CHARACTER OF GOD.
This then is the message which we have heard of him, and declare unto you, that God is light, and in him is no darkness at all. (1 John 1:5).
2. SIN IS THE TRANSGRESSION OF THE HOLY LAW OF GOD
Whosoever committeth sin transgresseth also the law: for sin is the transgression of the law. (1 John 3:4)
3. THEREFORE GOD'S WRATH IS REVEALED FROM HEAVEN AGAINST SIN
For the wrath of God is revealed from heaven against all ungodliness and unrighteousness of men, who hold the truth in unrighteousness... But after thy hardness and impenitent heart treasurest up unto thyself wrath against the day of wrath and revelation of the righteous judgment of God; Who will render to every man according to his deeds:...But unto them that are contentious, and do not obey the truth, but obey unrighteousness, indignation and wrath, tribulation and anguish, upon every soul of man that doeth evil, of the Jew first, and also of the Gentile... (Rom 1:18; 2:5-9)
So now that we know how God views sin, we can understand clearly why a penalty had to be paid.