God knew of His mercy. That He would be a merciful God on behalf of His human-being creation was a foregone conclusion. His mercy He would make the most of; knowing that He would allow sin to come into being.
The allowance of sin, of course, was to answer the accusations and doubts raised by Lucifer about God’s character and governance. Stopping sin in its inception by destroying Lucifer, its originator, would not have erased those accusations and doubts.
In fact, if Satan had been destroyed in the beginning, his allegations and suspicions would have been solidified in the minds of all the heavenly creatures.
Killing Satan at that time would have produced fear. Fear would have permeated all future relations with God. Worshiping, communing, and working with Him would be based on fear instead of love.
So the Lord allowed Lucifer to have his way so that all can see, and have answered for themselves, what it is like to live independently of His divine ways.
The first major glimpse of that was the war that broke out in heaven. Lucifer was quickly defeated, along with the angels he had persuaded to think his way. They were then cast down to earth where the spectacle of sin will complete its drama.
That’s where God’s mercy would be most helpful. He knew that because sin would infect human nature, we would all be born into that nature. Being born into a sinful nature was not our choice. And we all know how big God is on the matter of freedom of choice.
God is aware that it is not our fault that we are born sinful. This is something that He has allowed. Therefore, He determined to not leave us helpless. In the mercy of God, He has made sure that we are aware that we have the choice to pick between His righteousness and sin—between good and evil.
He’s done this by sending the Holy Spirit. The Holy Spirit is upon the earth to convict hearts of what sin is, of what righteousness is, of what judgment is.
God did not abandon us, leaving us to cope alone with His plan of allowing sin to have its season. He mercifully even sent us a savior—His own Son to die for our sins and sinful nature.
We have a merciful God because we ignorantly entered into sin, into unbelief. We are shown mercy because within His mercy, the salvific grace of our God is more than abundant, with the faith and love that is found in Christ Jesus.