Matt 20:1-16

This entire reading is a single parable. A possible name would be 'the laborers and the landowner.'
At an unspecified time 'early in the morning' this man hires men to work in his vineyard. I would think it was harvest...
The man keeps an eye on the marketplace, and at the third, sixth, ninth, and eleventh hours he finds more people to work, so he sends them in.
Now the agreement he makes with the first party differs with the others who come in later on. He says to the late comers "whatever is right" I will pay you. In vs 8 the setup is done and the outcome begins. This guy does something obvious, he just pays everybody the days wage. But that's not what the first outfit wanted to see. They protest in vs 12 'you have made them equal to us.' In short 'we worked harder.' And that isn't untrue.
Why is this ok? Well because the its really a sinners working for God scenario. We the sinners start out so far in the hole that just breaking even is impossible. The MDB remarks "everyone finishes in a dead heat." So verses 15 and 16 are really about God, who can do what He wants with what is His. I assume 16 is about God's judgment, being perfect there's no real telling who comes out on top when everybody's in such a state to begin with.