The awareness and understanding the concept of His oneness in the sense that there is no other like Him.
True fear of Heaven consists of understanding השגת יחודו.
The greater the understanding of hasagas yechudo, the greater the capacity is for fear of Heaven.
The evil inclination attempts to conceal hasagas yechudo by creating a situation of hiding His oneness by the creation of this world through the five senses, nature, and coincidence.