ועתה ישראל מה ה' אלקיך שואל מעמך כי אם ליראה את ה' אלקיך וכו' (י-יב)
מידה: יראת שמים
Moshe asks: “What does Hashem want from you?” What does He want? Nothing major, nothing too difficult. Just that we “fear Him ...” Sounds simple, right? And then .... Moshe continues with a long list of ideas: To go in all His ways; to love Him; to serve Hashem with all your heart and all your soul, etc. Moshe was telling the people that the most important pursuit in life is Yiras Hashem - Fear of G-d, and everything else follows. There are many explanations of what exactly this means.
The Chinuch equates Fear of G-d to fear of punishment. Hashem punishes man for all his sins. When a person is tempted to sin, he is obligated to fight his evil inclination by visualizing that he will be punished. But this is really the lowest level of Yiras Hashem. A higher level, as explained by the Mesilas Yesharim, and one that we should all aspire to, is the feeling of awe in G-d’s presence, by thinking about His greatness and how we are so small and inconsequential next to Him. Awe of Hashem’s great power will also cause one to be afraid of sinning. This higher level of Yiras Hashem is referred to as Yiras Haromemus - Fear of His Exaltedness. This causes a person to raise himself up above the nonsense of this world and become exalted as well.
All of our material accomplishments are meaningless. In the world of truth we will not be given credit for how much money we made. Hashem made it all happen through us. “What we have is G-d’s gift to us. What we are is our gift to G-d!” "הכל בידי שמים חוץ מיראת שמים" - Everything is in the hands of Heaven except for Fear of Heaven. The only real accomplishment that we may have in life – and truthfully the entire purpose of our lives - is attaining true Fear of Heaven.