From the looks of it, even though the newly acquired skill [Commandment: Punish] doesn't seem overly powerful right now, it will definitely boast a high usage rate given time. Moreover, it deals "true damage," which means "damage that ignores the target's resistance." The cost-effectiveness of this skill is simply off the charts.
This is exactly why Motan had that playful smirk just now—it's clear he realized the value of this skill.
Now, let's take another look at his quest panel...
[True Commandments]
Category: Special Quest
Quality: Legendary
Description: Fulfill hidden conditions to unlock the corresponding [True Words] for Commandment skills.
Reward: Special branch effects for the unlocked Commandment skills. For every Commandment skill whose True Words are fully unlocked, you will receive a [Commandment: Blank] and ???
Current unlockable True Words: [Commandment: Shield] 0/3, [Commandment: Barrier] 0/3, [Commandment: Punish] 0/3