فَلَا تَخْشَوُا النَّاسَ وَاخْشَوْنِ
Do not fear people; fear Me.
Lā takhshaw is a prohibition and ikhshawn is an imperative. The contrast operates upon fearing: human beings are not to be feared in this way, whereas reverence toward God is enjoined.
The two directions do not yield a logical contradiction because their objects differ. An accurate explanation must attend to the command, the prohibition, and the specific relationship each establishes.