והנערה טבת מראה מאד וגו' ותרד העינה ותמלא כדה ותעל (כד, טז)

And the maiden had a very good appearance… and she went down to the well and filled the pitcher and drew… (24:16)

A Mitzvah Done With Toil:

Chazal say that the water rose towards Rivkah the first time she went to draw it, but not the second time, as the pasuk says that this time she drew it herself. The Bais Avrohom explains that the first time she went to the well, she was getting water for herself, which was not a mitzvah. Since she was a tzadeikes, the water rose to her. The second time, she was doing the mitzvah of gemilus chasadim. Since a mitzvah done with toil and exertion is more valuable, the water did not rise on its own.