Here is the story. The people of Nineveh were very sinful but probably believed that nothing bad would happen to them. Jonah's message was simple. It was just this..."Yet 40 days and Nineveh shall be overthrown." The very next verse says..." So the People of Nineveh believed God" They changed their minds about being safe and and believed God that they were going to be destroyed. (they repented and had faith) So we have a simple message... then repentance and faith... then the fruits of that repentance and faith was works..... Jonah 3:10 "God saw their works that they turned from their evil ways"... and God repented (changed His mind) of the disaster that He had said that He would bring upon them.
So, there was real change, but out of fear, wonder how long it lasted?
Now there are four things that to me are interesting about this story....
1. It goes along with salvation or conversion stories. (by that I mean... people think that their sins are not that bad and therefore they won't be punished.... they hear a message that they are wicked and that God is going to punish them.... they change their minds (repent) and believe the truth (that they are sinners and God will punish them) and seek for mercy (faith) .... then works follow (they fast and turn from different sins and evil)
But we shouldn't serve or come to God out of fear, right? Love, if possible, right?
2. The second thing that is interesting is that this story most likely has absolutely nothing to do with justification or eternal life. Jonah's entire message seems to be "in forty days Nineveh will be overthrown". Did the people trust in a coming Messiah to forgive their sins and take them to heaven? Most unlikely. This was just a story about how God was going to destroy a city and the people did what they needed to do to avoid it and so God didn't destroy it. Nothing to do with salvation except for physical or earthly or political salvation.
3. Notice that it says that God repented. (KJV) God didn't turn from His sins (because He doesn't have any) He changed his mind. (Which is a figure of speech or an anthromorphism) Repent means to change your mind. Some versions say God "relented" but it is the same hebrew word that means to change your mind and is often translated repent.
4. That turning from sin is considered "works" by God. "Then God saw their works, that they turned from their evil way"
So, again true repentance includes true change, right?
God bless.