Last week I mentioned (link) the Brisker Rav’s question of why Avraham had to administer an oath to Eliezer to ensure that he look for a bride for Yitzchak only from Avraham’s own family – he could have accomplished the same by simply making Eliezer’s appointment as a shliach contingent on his going only to Avraham's own family. R’ Simcha Zisel (Kelm) asks this same question and offers a mussar-oriented answer. The oath was not needed from a legal standpoint, but was necessary from a psychological one. Avraham was so careful to make sure his wishes were accomplished reliably that he went the extra mile and added an extra safeguard to ensure their fulfillment.
There is an additional take away lesson from this episode. Eliezer, as we explained, was “moshel b’yitzro,” “doleh u’mashkeh m’toras rabo,” he was a righteous person in complete control over his desires, wholeheartedly dedicated to Avraham’s teachings. Is this is the type person who needs an oath to ensure that he fulfills his mission? The Beis Yisrael of Ger explains that Avraham knew that Eliezer was steadfast in his righteousness. However, Avraham was concerned that when distanced from his home, Eliezer would be tempted and tested by the spiritually hostile environment created by Besuel and Lavan. Therefore, he took the extra precaution of administering an oath.
The power of environment is emphasized as well in Avraham’s command not to take wife for Yitzchak, “M’bnos ha’Kena’ani asher anochi yosheiv b’kirbo.” Why does Avraham stress that he dwells among the Kena’ani – we already know this? The answer is that Avraham was acknowledging that his teachings would have little influence on a Kena’ani girl who, even if she enters Avraham’s home, would remain surrounded by the comforts of her original cultural milieu. No matter how great the message or the messenger, it cannot complete against an opposing message constantly reinforced by a culturally dominant majority.
A long while back we discussed the question of kids going to study at secular colleges far from home. I don't want to revisit it -- draw your own conclusions from these ideas.