There is a difference between ירא (fear) when the word את comes afterwards and ירא when the letterמ comes afterwards: ירא את is referring to the thing itself that one fears. And ירא מן is referring to the cause of the fear.

1 Samuel 14:26 says, ויבא העם אל היער והנה הלך דבש ואין משיג ידו אל פיו כי ירא העם את השבעה (And when the people were come unto the forest, behold a flow of honey; but no man put his hand to his mouth; for the people feared the oath), using the words כי ירא העם את השבעה for “for the people feared the oath”. This is an example of referring to the thing itself that one fears, namely the oath.

Deuteronomy 5:5 says,אנכי עמד בין יהוה וביניכם בעת ההוא להגיד לכם את דבר יהוה כי יראתם מפני האש ולא עליתם בהר לאמר (I stood between the LORD and you at that time, to declare to you the word of the LORD; for you were afraid because of the fire, and went not up to the mount—saying), using the words כי יראתם מפני האש for “for you were afraid because of the fire”. This is an example of referring to the cause of the fear, namely the fire.⁷²⁰

footnotes: ⁷²⁰ Malbim, HaTorah v’HaMitzvah Kedoshim 4.