the parsha of emunah

Why did Bnei Yisrael wait until after 40 years to sing shirah about the waters of the be'er? R' Leibele Eiger writes that the theme of our parsha is emunah. One must have faith even when things look bleak, even in the face of the incomprehensible. "Chukah chakakti, gezeirah gazarti -- ain lecha reshus l'harher achareha." What can look bleaker than the tumah of death itself, the focus of the parsha of parah adumah? Our parsha contains the death of Miriam and the death of Aharon, the loss of the be'er and the loss of the ananei hakavod. We read how Moshe is denied the opportunity to enter Eretz Yisrael. Yet, despite all these setbacks, the fact is that the be'er returned, the ananei hakavod returned, and there was a tzintzenes haman tucked away in safekeeping for all eternity. What appeared to be a complete loss was just that -- just appearances. That's what Bnei Yisrael sang shira for. The appearance of the be'er at the start of the journey in the midbar was miraculous, but the return of the be'er even after it seemed to vanish provided the knowledge that chasdei Hashem would be eternally present.