Or HaChaim on Deuteronomy 5:26/אור החיים על דברים ה׳:כ״ו

1 ליראה אותי ולשמר את כל מצותי, "to revere Me and to observe all My commandments." What is the reason that revering G'd does not include keeping His commandments so that the Torah had to mention it separately? Perhaps the reason is that fear of G'd resulted in a negative phenomenon when it became the cause that led to the making of the golden calf. When the people were afraid that Moses would not return, they were afraid that they no longer had an intermediary to whom G'd could speak to on their behalf. They feared that as a result G'd would speak to them directly as He had done during the first two of the Ten Commandments. At that time they had feared for their lives and begged for an intermediary. To forestall such a situation they hastened to make the golden calf as a substitute for the missing intermediary Moses. Tanchuma on Parshat Ki Tissa has told us that the calf actually spoke, thus lending credence to the belief that it was an intermediary. This is why G'd was specific, saying to revere Me as well as to observe My commandments. Henceforth reverence for G'd must lead only to observance of the commandments.

2למען ייטב להם, "in order that He will be good to them, etc." This means that the words: "who would give" were not said in order to describe the usefulness of such an attitude by the Israelites for G'd, but in order for the Israelites to reap the benefits of G'd's love which is the result of listening to His prophet.