GOD is so merciful. Right from the garden of Eden, He did not kill Adam and Eve outright or immediately as a literal reading of His prior Commandment would assume. Instead, He spared them. The edict against Cain was also reversed and He was not to be killed in spite of committing the dastardly deed of killing his only brother Abel.
GOD even warned Cain before this murder had occurred. This would mean that Cain would have found a lot of difficulty in a Court of law, to defend his actions. More so, GOD also notes that Abel's blood was "testifying from the grave" and seeking for justice. Cain was therefore doomed - save for the mercy of GOD who even amended his edict by ensuring that Cain is branded clearly so as to avoid being killed by anyone as he sojourned the earth as a fugitive.
Enter "Father" Abraham - who is probably the first known earthly Advocate in the Judeo Christian accords. He seeks to advocate for the forgiveness of Sodom and Gomorrah from total destruction in case there are a few good men in the City. He probably was mindful of the fact that his nephew Lot resided in that place. Once again we see the merciful hand of God who allows to be convinced to forgive. Even Lot negotiates for a nearer place of refuge to avoid destruction. This is because GOD had told him to go to a further place
The above characteristic of GOD is what seems to frustrate Jonah. He shows his unwillingness to preach death and destruction to the people of Nineveh because he knew that God would turn around in case the people repented.
All through the Bible, we clearly see GOD extending mercy again and again. This speaks to his character and methodology. A merciful God who is ever willing to reconsider His judgement in case a sinner repents. This is therefore why JESUS CHRIST also came to earth to die for our sins. That is the ultimate show of Mercy and a merciful God. Amen