And with Him are the keys of the unseen treasures – none knows them but He; and He knows what is in the land and the sea, and there falls not a leaf but He knows it, nor a grain in the darkness of the earth, nor anything green nor dry but (it is all) in a clear book. (6:59)
What is evident in the verse is exclusivity in the knowledge of the unseen by the statement – none knows them but He.
So Allah exclusively knows the unseen. He knows the sublime and subtle issues and He neither misses nor forgets anything. This is elaborated by the words – with Him are the keys of the unseen.
What was the purpose of beginning the verse by the statement, And with Him are the keys of the unseen treasures? By this statement, He clarifies control on the knowledge of the unseen and that His knowledge encompasses everything.
Although the above verse is translated as “With Him are the keys of the Unseen”, it is also correct to say: “With Him are the treasures of the Unseen” because the conclusions of both statements are the same. Whosoever has the keys of the treasures is aware of what is in them and has the power to use them as he pleases just as the one who has the treasures.
In any case, no one has access to those treasures since he does not have knowledge of their keys by which he can open them and use what is therein. This is the gist of the first part of the verse.
From another angle, the first part of the verse deals with the unseen which are not entities that can be comprehended by visible boundaries nor can they be quantified by known measures. It is true that we cannot comprehend anything unless it is limited and measured. That is why in 15:21, Allah says:
And there is not a thing but with Us are the treasures of it, and We do not send it down but in a known measure.
The things in the treasures of the unseen, before they descend to the level of visibility and measure, are without boundary and measure even though they exist in some kind of an abstract form with Almighty God.
All entities that are visible in this world, before descending, existed with God in His treasures and we are unable to comprehend their form of existence.
Perhaps there are other things preserved within these treasures that are not comparable to things that are known to us. This kind of unseen that has not emerged on scene of visibility is known as “the absolute unseen”. Things that have emerged from the unseen, in a known measure, but still not visible to us are termed as “relative unseen”. For example, there is something inside a house, it is seen in relation to those who are inside the house and it is unseen in relation to those who are outside it. To a blind person, the things that are visible to us are “relatively unseen” to him.– Allamah Tabataba’i
What God mentions in the latter part of the verse, and He knows what is in the land and sea, and there falls not a leaf but He knows it, nor a grain in the darkness of the earth, nor anything wet or dry but (it is all) in a clear book, refers to the relative unseen since all these items are limited and measured that can either be comprehended by us or they could be hidden from us.
Reference: Al-Mizan, English Vol. 13