This wise saying is about bad people – “whoever sows injustice.” The verse says what most of us already know – it will not got well for these folks.
To “sow injustice” would be to do things displeasing to God and hurtful to people. Sowing is planting – if we plant bad stuff we can only expect to “reap” or harvest some of the same.
In this case, it’s “calamity.” The Bible is pretty clear about all this – “we reap what we sow.”
“The rod they wield in fury” would be the inappropriate motives and actions of these folks toward others. While God is not mentioned in the verse, there’s little doubt that He’s the one who will make sure their rod “will be broken.”
This verse can be taken as God’s promise that no one gets away with injustice or their fury. That’s the good news.
The bad news is that it applies to me, my motives and my actions, too!