We learn an important yesod from here. Even though Avraham had no contact with Nachor for decades (Netziv explains that this was the intent of "Lech lecha... m'beis avicha"), a brother is still a brother, and all the shefa, bracha, and benefits that came into the world because of the tzidkus of Avraham Avinu overflowed and benefited Nachor as well. They of course probably never suspected that as the cause, but, "Nachor achicha...," when you are related to the tzadik ha'dor and have even a small connection, good things rub off and come your way.
It is nice to pat yourself on the back and think that if things are going well it is because Hashem is getting nachas ru'ach from your avodah. But the truth may be that your second cousin twice removed, or even a stranger who you don't even know, is such a tremendous ba'al chessed, ba'al avodah, etc. that the whole world benefits from -- including you.
On the other hand, who knows? It could be your tefilos, that you don't think are having any effect, are benefiting a Jew somewhere in the world who really needs it.
We see the same idea in our parsha. "Hinei Rivka yotzeis asher yuldah l'Besuel..." Why the passive voice, "yuldah?" Kedushas Levi explains that Rivka may have biologically born to Besuel, but what caused a girl like Rivka to come into the world was the chessed of Avraham miles and miles away. Besuel reaped the results, but the cause of events was Avraham Avinu.
Eliezer says that if the test he devised to find the right girl works out it proves, "ki asisa chessed im adoni." (24:14). G-d was not doing chessed "l'adoni" = for Avraham, i.e. giving him a gift, but rather "im adoni" = with Avraham, i.e. the chessed Avraham himself did was what created and set in motion events leading to Rivka.
How does this work? The way Hashem interacts with a person mirrors the way that person interacts with the world. For example, Chazal say that a person who is ma'avir al midosav, who is forgiving, will have his/her own sins forgiven. But it goes beyond personal benefit. The way Hashem interacts with the whole world changes. The chessed of Avraham opened a channel of chessed -- there was more chessed coming down to the entire world. That abundance of chessed caused a Rivka, another ba'alas chessed, to develop.
This idea can also shed light on how Eliezer managed to have such tremendous success Eliezer had on his mission. Ya'akov Avinu, the paragon of emes, had to spend 14 years in Yeshivas Shem v'Eiver preparing himself to deal with the cheat and liar Lavan. Here, Eliezer walks into the lion's den and walks out with Rivka on the same day. How did that happen?
Chazal tell us that Eliezer had a daughter of marriageable age who he would have loved to see married to Yitzchak. Shem m'Shmuel writes that this was not a coincidence. Hashem was using reverse psychology in placing him in this situation. Davka because Eliezer faced the temptation of not being true to Avraham and to his mission made him that much more on guard and dedicated to carrying out his shlichus faithfully. When a person makes such a great effort to be true to his master, his mission, in turn Hashem mirrors that and more truth and faithfulness come into the world. That extra burst of truth energy, if you will, is what enabled him to overcome Lavan.