Ecc 8:5 Whoso keepeth the commandment shall feel no evil thing: and a wise man's heart discerneth both time and judgment.
In context, if we could say there is such a thing in this poetic book, the commandment probably deals with whatever a sovereign instructs his subject. However, I can imagine it meaning the first and great commandment upon which hangs all the other commands.
Mar 12:30 And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment.
Are we whole-heartedly loving the Lord? Can we say also, "whole-souly" and "whole-mindedly" and "whole-strengthedly"?
This is not a suggestion but a command. God will accept nothing less. He is not "understanding" of our meager attempts at loving Him. He wants it all and is jealous over the matter.
Keep THE commandment.