|Art: William Adolphe Bouguereau|
"The servant ran toward her" [Chayei Sarah 24:17]
Rashi comments: "Because he saw that the waters went up toward her".
Where does the verse indicate, asks the Ramban, that the waters actually went up toward her?
Later on, answers the Ramban, the verse states: "She drew for all his camels" [24:20]. In this verse, however, we find no mention of Rivkah "drawing" any water. This teaches us that Rivkah, in fact, had no need to draw water for the water rose up toward her.
Yet, asked R' Levi Yitzchak of Berdichev, why did the water not rise for her when she drew water for Eliezer's camels?
Initially, Rivkah had gone to draw water for her own personal needs. In order that the tzaddekes should not have to burden herself with the task of drawing water, the water, instead, rose to her. However, when Rivkah went to draw water for Eliezer's camels, she had undertaken to perform a mitzvah. Heaven wanted Rivkah to earn as much merit as possible for her act of kindness, so, this time, the water was not allowed to rise for her. In this way, Rivkah would receive maximum merit for performing this mitzvah, for as Chazal teach us, "According to the exertion is the merit". [Avos 5:26] Thus the more she exerted herself, the more merit she would receive.
Source: Rabbi Yisrael Bronstein