In scripture there are many seeming inconsistencies and using certain reading strategies these are insuperable.
One of these strategies is the one in which we take everything literally.
For instance we have this verse from Numbers:
“God is not a man, that he should lie; neither the son of man, that he should repent:” Numbers 23:19
But we also have verses like this:
“for I knew that thou art a gracious God, and merciful, slow to anger, and of great kindness, and repentest thee of the evil.” Jonah 4:2
Here Jonah is explaining to God why he went to tarshish instead of Nineveh. God had said He would destroy Nineveh and Jonah wanted Nineveh to be destroyed. That destruction was the evil that here – according to Jonah – God would and did repent of.
So the question is did God actually change His mind or was His intention fully carried out with no deviation? Which one glorifies God?
To settle the matter I will bring in the verse I believe to be of the highest authority in all of scripture. A verse that is as literal as it gets:
“For of him, and through him, and to him, are all things” Romans 11:36
For god to change – truly change – His mind (to repent) there would have to be an agency outside of Him that could throw curve-balls his way.
God would have to be such a being that certain events surprise him and force Him to change His plan to accommodate a fluid situation.
For a human this way of acting, this way of being fluid is laudable. No plan survives contact with the enemy after all.
But all things are not from, through and to us.
We exist in a state where there is a reality outside and – in some senses – against us to which we have to accommodate our wishes and plans.
But God is not a man.
So why the apparent change in His plan?
Because His real plan, His unchanging will was here to use Jonah and Nineveh as a means to express His divine character. He expressed His love through an apparent change of mind.
Nothing expresses Love like leniency!