Lech Lecha: A True Eved Hashem

Leaving Charan is counted among Avraham's ten tests. But if Hashem Himself told any of us to leave home, circumcise ourselves or bring a son, wouldn't we simply obey? What made these tests so hard? The Gemara in Berachos has Yeshayahu telling King Chizkiyahu he will lose his place in the World to Come, and the reason is surprising. Rav Chaim Shmulevitz reads it as the key to Avraham's tests, and even to Shaul's lost kingdom and the drinking of Purim. Where does "doing the math" quietly cost us our service of Hashem?