In America and other places in the Western world, oath-takers raise their right hands and pledge to perform certain actions, sometimes placing their left hands on a Bible. On other occasions, people promise to do something—pay back a loan, perform a service, hold wealth in trust, etc.—by signing their names to a legal document before witnesses. Some promises are made with a Boy Scout oath. Young girlfriends make pinky promises.
These were not the norm four thousand years ago in the land of Canaan. As the Old Testament attests, oaths and vows were taken far more seriously than they are today in our winner-take-all, I'll-do-what's-best-for-me world. One's word was truly his bond, and oaths were not to be taken lightly or frivolously. In some modern Bibles, "oath" or "vow" is often accompanied by a modifier like "solemn," especially since they usually invoke God to bind them on the oath-taker.
The next two verses confirm Abraham's reason for requiring his servant's oath: "I will make you swear by the LORD, the God of heaven and the God of the earth, that you will not take a wife for my son from the daughters of the Canaanites, among whom I dwell; but you shall go to my country and to my family, and take a wife for my son Isaac” (Genesis 24:3-4). The patriarch desired to bind his servant to his wish to have his son marry a daughter of his own people, a woman from among those who had migrated with Terah and Abram to the area of Haran in Mesopotamia. There was no stronger way to bind him than to have him make an oath with his hand under the patriarch's thigh.
We see the same kind of oath in Genesis 47:29, when aged Jacob requires Joseph to promise to bury him in Canaan. In both situations, the instigators of these oaths are patriarchs of a clan, and it is this fact that provides understanding about the symbolism of placing a hand "under the thigh." The IVP Bible Background Commentary: Old Testament fills us in on what this placement represented: "by placing his hand inside Abraham's thigh (in the vicinity of or on the genitals), the servant ties his oath of obedience to the acquisition of a wife for Isaac and thus the perpetuation of Abraham's line."
Evidently, this kind of oath—called by some a "bodily oath"—was made for matters pertaining to the most important family and clan matters. Abraham's oath is easily seen in this light, as he desired his only son by Sarah, his heir, Isaac, to marry and have children from among his own people, those from the line of Shem and Eber (the progenitor of the Hebrews). He binds his servants actions on his behalf to considering young women only from that narrow ethnic group.
Jacob's demand for a similar oath is more difficult to explain, but he, too, requests it for the good of his clan. The patriarch knew the prophecy God gave to Abram in Genesis 15:13-21, that his descendants would "be strangers in a land that is not theirs. . . . But in the fourth generation they shall return here." Jacob's desire that his bones be buried in Canaan makes a statement that the land of Goshen, where the children of Israel were then living, was not the tribal inheritance of Abraham's people, but they must return to the land of Canaan, where the bones of Israel were interred. Later, Joseph also told the Israelites to "carry up my bones from here" (Genesis 50:25), passing to the next generations the expectation of returning to Israel's promised land.
Faced with fulfilling such a solemn oath, Abraham's servant, likely Eliezer of Damascus (Genesis 15:2), takes great care to choose a suitable mate for Isaac, placing his trust in God to lead him to the right woman. In fulfilling his oath, Eliezer is blessed by God and led directly to the family of Nahor, Abraham's brother. And so, in the course of events, Rebekah travels to Canaan with Eliezer, marrying Isaac, and perpetuating the line that ultimately leads to Jesus Christ.
Richard T. Ritenbaugh