Jesus told a very short story about the kingdom. A man had two sons. He told both of them to go work on the farm. One son refused, but he later regretted what he said and went to work. The other son agreed to go, but he never went. When we consider which son really obeyed his father, it would be the first son.
The essence of the kingdom is pleasing the Father. It is not what one says; it is what one does. The religious leaders, Jesus was talking to, talked a good game. Some worked hard at obeying the religious rules. But they ignored the thing God considered of prime importance, mercy, and humility.