The difference between Simeon and Herod lies not in understanding but in response: where Simeon replies to the news by joyously affirming, “we are bold to say that we have seen our salvation,” Herod replies with blunt opposition: “I refuse to be taken in.” With a sigh of deep regret, he orders the slaughter of the Israelite children.
Simeon the theologian may have found it difficult to accept the idea of God Incarnate, but for Herod it is impossible, because acceptance would require him to relinquish his position as the chief local instrument, in Judaea, of Romanitas and the Caesarist project. And this he lacks the strength of will to do.