Why, the rabbis ask, did Abraham only now, at the border of Egypt, realize that Sarah was beautiful? Had he never noticed before?
One reading of (Genesis 12:11) goes like this. Abraham says, Behold now I know that thou art a fair woman, meaning: most travelers lose their bloom on a long and dusty journey. You, Sarah, have not. The desert has not touched you. And that is when I truly understood how beautiful you are.
A second reading is stranger and more tender. Abraham was so modest that in all his life he had never once looked at a woman's face, not even his own wife's. They had lived decades together, and he had never studied her features. Only now, as they crossed a river near the Egyptian border, did he glance into the water, and there, rippling in the current, he saw the reflection of Sarah's face for the first time. Behold now I know that thou art a fair woman. He had been married to her for years before he ever saw her.
Abraham knew the Egyptians well. They were a swarthy people, and a woman who looked like Sarah would not go unnoticed in Pharaoh's court. So he did what a man can do when prayer and flight have run out. He hid her. He built a wooden chest and smuggled her across the border inside it, hoping to slip past the king's agents unseen.
It did not work. The officials opened the chest at customs. But this passage from Hebraic Literature (1901) wants us to notice the man before the failure: a husband so modest he had to see his wife in a river, and a prophet so practical he built her a box to hide in.