God Almighty has His own prerogative to devise His divine plan and pass His divine Law which mankind cannot question Him as the Almighty. He knows what is best to carry out His will.
Based on what God revealed to mankind in the Holy Bible, this is the account which has been made known:-
God sent His own Son JESUS because the first man ADAM had failed the Test by SATAN. His Son was commissioned to wrestle from the SATAN all areas which were "captured" from man. Sins are the consequence of Adam's failure to obey GOD, not to fight sins but to fight against SATAN.
If GOD did not send JESUS to fight against SATAN - the chief agent of sin to enter the World, then who will destroy the works of SATAN???
God is a Righteous GOD and He will not destroy SATAN without principle and follow His own Laws. His Law says the penalty of sin is death. SATAN knew the law and it means ADAM and EVE have to die because of their sins. Both of them died and their bodies returned to the dust of the ground. How about their souls which will not die unless GOD destroy them in Hell?
Now someone who is sinless or without sin can destroy SATAN, the master of sins. You cannot use sinful man to atone the sins of people. The only solution is to use the Blood of the sinless Man to destroy the works of SATAN. So GOD have to become a Man and the mission is accomplished by HIS SON JESUS.
If GOD change His Law or pardon Adam and mankind for their sins, the ransom must be paid by someone. You know about Blood-money for those who are intentionally killed by another man. Why the Blood-money??? The principle of GOD is the same. Blood-money have to be offered. So whose Blood-money will fulfill the law. None except LORD JESUS' Blood who is sinless.
God has provided sacrifice for Adam and Eve when they sinned against Him in the Garden of Eden.
God has also provided sacrifice when Abraham was about to sacrifice His own son (Which sons is not the issue here).
God has sent His Son JESUS as a sacrifice for His People. His People are the Jews and all those who accept Him as Lord and Saviour.
GOD is a Judge of Justice. He have to answer to SATAN if He did not obey His own laws. SATAN will scorn at GOD for being a liar if HE simply pardon without keeping His own words. So how could GOD punishes the sins based on His law and pardon the sins when His own law requires the shedding of Blood for remission of sins?
Heb 9:21 Moreover He sprinkled with blood both the tabernacle, and all the vessels of the ministry.
Heb 9:22 And almost all things are by the law purged with blood; and without shedding of blood is no remission (of sins).
Mat 26:28 (JESUS said) For this is my blood of the new testament, which is shed for many for the remission of sins.
If you were GOD, then answer it in the best way which shows justice and truth to his own laws.