"The human mind can only recognize the truth, not govern it"
Our mind typically views truth as a sort of commodity, a useful thing that can be measured, evaluated, or manipulated – and when inconvenient or contrary to its agenda, simply set aside. Truth has value too, considering its power to enlighten, so it's a commodity to be controlled and kept from the competition. It's as if our mind sees itself as independent of the truth, with the power to invent, shape, decide, control, modify, and manage it (etc. – see synonyms for 'govern').
This is a strangely myopic view in that everything the mind actually experiences is of the truth, albeit a very specific and limited sample of it. Our thoughts, no matter how quixotic, are nonetheless truthfully perceived. Our misperceptions are truthfully misperceived, our delusions truthfully embraced, and our lies truthfully delivered and accepted. Truth, synonymous with reality (see synonyms for 'truth'), is the very context of the mind's existence, its venue of perception. So no, the mind all by itself can't handle the truth – literally speaking.
Therefore this aphorism encourages our mind to simply recognize the truth as it is rather than futilely and tragically attempt to govern it.