To have mercy on someone is to pull back from hurting them because you love your neighbor as yourself. You would not want a more powerful person to harm you, so you don’t do it to someone else. If a higher authority than King Herod had decreed that King Herod should be captured, tortured, and killed, Herod would likely beg for mercy. It is hypocrisy to be merciless toward others but expects mercy for oneself. The law remains: you reap what you sow.