“Is repentance a work? Jonah 3:10, to me, looks like to say that repentance is a work. Please correct me if I am wrong.”

Thanks for your question!

For a long time, I had trouble understanding how we “repent and believe” and yet, in doing so, do not perform any work that merits salvation (Mark 1:15). Over time, I came to understand that belief or faith, as it is commonly put, is not some magical force we muster up ourselves, but it is a gracious gift of God that He gives to His elect so that the works of Christ will save them (Romans 5:1-11, Ephesians 2:1-10). 

However, I still had a hard time understanding how repentance wasn’t a work. After all, repentance is an action, right? Well, it’s actually not. Given how the book of Acts focuses on the command to “repent” more often than to “believe,” it may seem that the two are separate commands or concepts (Acts 2:38, 3:19, 3:26, 8:22, 9:35, 11:21, 14:15, 15:19, 17:30, 26:18-20, 28:27). Well, they’re actually not separate. 

What changed my understanding of repentance is recognizing that repentance and faith are inseparable. They are like two sides of the same coin; you cannot have one without the other. One cannot exist without the other. In Acts or any other book, the commands to “repent” and to “believe” are simply shorthand for “repent and believe.” 

Furthermore, no sinner repents and believes in God for salvation unless He first regenerates them, granting the sinner faith and repentance through the gift of a new heart that desires God and recognizes sin for its wickedness (Ezekiel 36:26, John 6:65). 

Though repentance itself is not an action, like faith, it leads to good works. To repent and believe is to have your heart, affections, thoughts, and desires changed from unconditionally loving sin and darkness (John 3:19-21) to trusting in God alone for salvation, which leads to good works that God has prepared for us (James 2:14-26, cf. Eph. 2). 

In a posted Got Questions article, the author wrote, “While repentance is not a work that earns salvation, repentance unto salvation does result in works. It is impossible to truly change your mind without changing your actions in some way. In the Bible, repentance results in a change in behavior. That is why John the Baptist called people to “produce fruit in keeping with repentance” (Matthew 3:8).” 

Now that we have walked through what repentance is and see that it is not a work, let’s look to Jonah 3. Rather than speaking of eternal salvation, this passage is likely speaking of temporal, physical “salvation” or, in other words, that God would honor Nineveh’s repentance and not carry out His judgment despite their previous sins. As David Guzik puts it, “We do not obligate God to forgive us when we repent. Instead, repentance appeals to God’s mercy, not His justice.” Also, God did eventually judge Nineveh 150 years later, as noted in Nahum 3.  

Secondly, we should understand God that God “relented” (other translations say “repented”) in light of His immutability (the attribute of God that refers to His unchangingness, that God does not change). His will for Nineveh never changed. At times, Scripture uses this sort of language to help us humans understand the nature of God. In a more complex way of putting it, Albert Barnes writes, "As God is unchangeable in nature, so is He unchangeable in will. For no one can turn back His thoughts. For though some seem to have turned back His thoughts by their deprecations, yet this was His inward thought, that they should be able by their deprecations to turn back His sentence, and that they should receive from Him whereby to avail with Him. When then outwardly His sentence seemeth to be changed, inwardly His counsel is unchanged, because He inwardly ordereth each thing unchangeably, whatsoever is done outwardly with change." 

In summary, repentance is not a work, but is perfectly intertwined with faith and is brought about by God. When we repent and believe in Him for salvation, we don’t change His mind, we are fulfilling His will that He is carrying out. He is sovereign over all, and we should take great joy in being so graciously and unconditionally loved by the One who rules it all. 

Feel free to submit a follow-up question if anything needs to be clarified or answered. Thank you!