Measure for Measure

Rabbi Moshe Ben-Chaim

This means that God will judge the person in the person's own terms. For example, the Egyptians had drowned the Hebrew infants, and they met their own fate at the Red Sea when they were drowned. The reason for this parallel is not poetic, but to alert the sinner and others to the source of his crime, which is used in his punishment. Yisro said, 

Now I know that God is greater than all gods, through His punishment that matches their crimes (Exod. 18:11).  

Rashi comments:

By that very thing with which the Egyptians thought to judge Israel, were they themselves judged: they had thought to destroy them by water and they were themselves destroyed by water.

Rav Huna had 400 barrels of wine that spoiled and turned to vinegar (Brachos 5b). When his friends ad vied that God does not punish without cause, and that he should look into his ways, he discovered that he had withheld the vines from his tenant farmers. His friends advised this was an error. When Rav Huna repented, God returns his loss and reverted the vinegar back into wine, others say the value of vinegar rose in value to that of the value of wine. Either way, God returned his loss when he repented.

These two cases are a sampling of all others where God intends to help the person correct themselves by pointing them to the area of their flaw. The punishments were meted out in the very area of the sin, water for the Egyptians, and wine for Rav Huna. And when one repents, there is no longer any purpose to his loss or punishment, so God returns his loss.