I am not sure if you are looking for a specific answer from your textbook. Here is a general answer. I think that if ordinary people are unaware of the greatness of God, it is because they cannot conceive of God. They cannot possibly understand God, because of the smallness of our lives as humans.
You are going to receive different answers to this question based on the particular context of the answerer, to be honest - everyone will have a different view on what prevents us as a species from comprehending the greatness of God. One answer might be that we are so focussed on being God-like ourselves and achieving independence that we are unable to comprehend our inherent dependence on God. Emphasis is placed on us being in control of our own lives in the West, so it is hard for us to comprehend our absolute dependence on God. This of course, is my "reading" of your question though - others may well disagree.
That is an honest question. People have different notions about the divine, because of various reasons. First, you need to start with whether people even believe in a divine. Some people are atheists. In this case, you need to ask why some people believe and other do not believe. Second, if people believe in some sort of divine, then you have to be aware of the fact that people have different traditions and experiences. Based on this, their understanding of the divine will change. However, this fact should not lead you to despair. Conversations could start and through these conversations people can begin to explore their reasons and beliefs about the divine.
Seeing that the question derives from a textbook, I think that some level of further inquiry into this source is needed. Certainly, if the answer is within that and this is the model on which you are being assessed, I would examine it in a thorough manner. Outside of that, a potential reason as to why individuals could remain unaware of the "greatness of the god" could be due to the fact that the power of the divine is inconceivable to the mortal. Simply put, the awesome power of a power of divinity might represent both terms. "Awesome" in its scope to inspire awe and "power" as in an external exercise. Both might be impossible to conceive within the mind of the mortal. The creation of the cosmos, as suggested in the previous response, could be one such domain where its origin and the ability to create it would be far beyond the capacity of the mortal individual. Consider also the scope of time embraced by the divine. Some modes of spirituality argue that the time inhabited by their forces of the divine range into the hundreds of thousands of years, and in some cases, even millions of years. In some narratives, the unit used to measure time is beyond years, as Geologic Eras are reduced to a mere day. This lies outside of the reach of individuals, and the inability to conceive on such a scale might be a reason why there could be an unawareness of the power and greatness of the divine.
The biggest problem of becoming aware of greatness or otherwise of of God is the problem of reaching an understanding of the god itself. Different religions and different cultures have highly divergent concept of God. To be able to assess the reality and greatness of God we need to first be first clear about what we mean by god.
Some of the prevalent concepts of the nature of god, such as those of gods in Greek mythology, with qualities like their jealousies and craving for worldly pleasures, do not inspire very much the feeling of being all that powerful or respectable. Besides it is very doubtful if they exist now, or ever existed in the past.
There are other concepts of God which simply cannot be refuted logically, and there can be no doubt about the greatness of such a God. For example, one concept of god is the power behind the existence of this world. We do not know what this power is, but if the world exists something must have caused it, even if that something is the nothingness of Hindu philosophy. This concept that this entire universe gas grown out of nothing is now even confirmed by the widely accepted scientific theory of big bang. If we accept this concept of God then our awareness of greatness of God can only be limited by our ability to imagine what greatness means.