“The secrets belong to God, and the revealed things are for us and our children forever, in order to follow the words of the Torah” (29.28).
Rashbam takes this to mean that God will punish on the basis of secrets that He alone knows. Humans punish according to human law that has been revealed on Sinai.
Nachmanides, takes this to mean that God will know if you are sincere or not.
It can however mean something very different. The Talmud in Hagigah says that it is pointless to try to discover “what is above and below, inside and behind.” Given that the rabbis of the Talmud were quite scientific and empirical in their approach to life and their emphasis on studying the stars and the heavens, it is unlikely that this meant, don’t explore the universe or be concerned with inner secrets. Although in this context it is just as likely that it is a warning against esoteric mysticism, the Orchard.
I think it does mean that there are things we cannot know even if we should go on trying to find out. But given the fact that we are constantly learning and revising and searching it is inevitable that there will be things we still are uncertain about in our physical universe. The only certainty is that we are here at this moment and that we have to do our best to use our potential. To do this we need a guide, a moral code. is the Torah that is not secret but has been completely revealed to us.