In Genesis, chapter one, the six days of creation are described. Each day highlights the element(s) and/or life that are created. In the case of all but one and a half days, God labels all of His creations good, with the exception of day 2, heaven, and the latter half of day 6, man.
It's often wondered why two of God's creations are not explicitly labeled "good". The purpose of not labeling them would appear to be to create wonder regarding their lack of assigned label.
The first chapter introduces elemental concepts regarding how to read Torah/Tanahk/Bible. One of the first and most important concepts is to understand that God didn't give us a book of dogma to blindly follow. While not labeling day 2 and half of day 6 is not the first mystery, for many it is the first obvious non-declarative mystery.
Why would God create mystery within the very beginning of creation? We learn by wonder. The result of wonder is curiosity. Without curiosity, we don't look deeper into the text to see if we've overlooked something, if we've made a mistake, if the text was translated right. Until we start looking, we don't find the limits of our knowledge. If we don't find the limits of our knowledge, we may never question ourselves. If we don't question ourselves, how can we ever go in search of a knowledgeable source to query?
In the beginning, God appears to be showing us, by omission, that we have limits. Further, God appears to be teaching us to wonder, be curious, ask questions, and look deep into the text for answers - to reread what we've covered or be patient as we continue reading material (whether new or familiar.) More so, when we aren't certain, God appears to be teaching us to find a source to ask. Finally, God appears to be teaching us to look to the ultimate source of wisdom for answers when we can't find them on earth - through prayer to God.
In the case of creation, verse 31 of Genesis chapter one states that God sees all He's created and it was very good. In this case, we are free to use the math of Sets to view the days of creation:
Good days: { 1, 3, 4, 5, 6 (1st part }
Very good days: { 2, 6 (2nd part), all good days }
What we're left to wonder about is why God waits to label heaven and man until the end of the chapter, correlating to the end of His creating. Is it because God uses an economy of expression in His writing? Is it because heaven and man need to grow into their potential until God sees they are, in fact, very good? There are an infinite number of questions that we can ask.
If we look to Genesis 1:1, in which God begins to create heaven and earth, we may see a hint. Perhaps at the time that man grows the wisdom to live in accord with the laws, commandments, and prophets brought to earth from heaven, then God will see all of His creation as very good. Though it's always possible both heaven and man were very good when created.
Maybe the point and purpose is to create the curiosity to keep reading God's word, wondering, learning, asking, discussing, praying, and growing until we find the answer or answers? If we keep trying, we'll eventually find answers.