The positive mitzvot occupy the realm of the apprehensible, they can be grasped and understood, on a human level at least.
The negative mitzvot are only partly knowable, and that only as an interdiction, a ban on action or thought.
They are clear only in what they disallow, there is no hint at the possible damage or perils involved in doing the wrong thing.
It may be compared to the instructions given to someone who is blind.
One can explain that it is dangerous to walk past the curb, one cannot show the blind man the passing vehicles that make it dangerous.
Words of warning are almost always bigger than our capacity to absorb them, so that we have to leave a certain space, a negative absence of comprehension.
Thus the negative mitzvot are powerful in what they leave unsaid.
They are on a higher level than the positive mitzvot because they are closer to the realm of the hidden and the holy.
–Rabbi Adin Steinsaltz
From “Sanctity and Restraint” in The Candle of God by Rabbi Adin Steinsaltz