No one says "all is unknowable". The future is unknowable. But the past is not, especially well documented historical events.
Yet we are inundated daily with people claiming truth that should be followed by all because they have correctly interpreted the will of god.
We should be suspicious of people claiming to divine the future based on Biblical prophecies, because those things are truly unknowable.
But there are several other very plain assertions in the Bible that are injunctions or commandments whose meaning is quite clear. Such as "Do not kill", or the golden rule, or "Pray to God."
Yet this is a thread about biblical prophecy.
If it’s unknowable, what’s the point?
Don’t kill or treating people with respect doesn’t require a god to come up with.