Love for G-d is limited by its own size. When we confront an obstacle greater than our love, we need something stronger to catapult us. Isaac's abnegation of self and strict code of obedience shifted his focus from himself onto G-d. Thus he was able to "unplug" Abraham's wells
This is not a question about why people choose to do evil or why evil is visited on the innocent. It is a broader question. Why did G‑d create evil and what purpose does it serve?
Esau was understandably perturbed over losing the blessing. But why was he suddenly concerned over his birthright? He had surrendered it with barely a protest years earlier, so what changed now?