Genesis 24:2

Eldest servant. The most trusted servant of Abraham’s house was Eliezer (Patriarchs and Prophets, p. 173), who half a century previously had been tentatively selected by Abraham as his prospective heir (Genesis 15:2). He was now summoned by Abraham for a most important mission.

Thy hand under my thigh. This ancient ceremony accompanying a solemn oath is mentioned again only in Genesis 47:29. In both instances the circumstances suggest a promise to deal faithfully after the death of the one to whom the promise was made, that is, with his posterity. The death of the one would not release the other from his oath.

Explanations of the custom vary somewhat among commentators. As the source of posterity (see Genesis 35:11; 46:26; Exodus 1:5), the word “thigh” or “loins” (same word in the Hebrew) has been considered as pointing to Abraham’s future descendants, in particular to Christ, the promised Seed. If so, the oath was, as it were, sworn by, or in the name of, the One that was to come. Other interpreters have considered the thigh as symbolic of lordship or authority, and the placing of the hand beneath it an oath of allegiance to a superior.