So at 40 years, Joash had a pretty long reign, especially compared to what we have been seeing lately. However, he was still murdered in bed before he was 50. But let's not get ahead of ourselves.
Joash performed acceptably as king as long as Jehoiada was alive. After Jehoiada dies, Joash starts listening to the people who want to worship idols and abandon the Lord. Now, the chronicler wants us to think this reflects badly on Joash, but I think Jehoiada also deserves some of the blame.
Joash became king at age 7; obviously, Jehoiada was doing most of the ruling at that point. Furthermore, Jehoiada had a lot of control over Joash personally; this can be seen in the fact that the priest chose two wives for the king. Thus, it seems likely that Joash never actually learned how to rule. He only learned how to follow. Once Jehoiada died, Joash just followed the next people who were willing to take charge.
After Joash, his son Amaziah rules. Amaziah is another decent but not great king, according to the chronicler, but based on everything we see, he seems rather bad. Violence and war characterize Amaziah's reign. He shows some success and some trust of the Lord in his defeat of Edom (throwing 10,000 prisoners off a cliff in the process), but then he turns to idols and earns God's anger.
God uses Israel to teach Amaziah a lesson. Israel defeats Judah in battle and ransacks Jerusalem. However, Amaziah lives for a good while longer until he is eventually assassinated like his father.
Today Paul conveys a number of moral lessons to the community of believers in Rome. Lots of good generic advice such as: evaluate yourself truthfully, take advantage of your natural talents, love each other, work hard, be hospitable, live in harmony, don't be proud. Good advice that applies even to those outside of Paul's target audience.
Psalms and Proverbs
Today's third proverb is pretty good:
False weights and unequal measures—
the Lord detests double standards of every kind.