His eldest servant of his house; viz. Eliezer, Genesis 15:2. This ceremony was used in swearing, as now, so anciently in the eastern parts, as Genesis 47:29, either as a testimony of subjection, and promise of faithful service, for this rite was used only by inferiors towards superiors; or, as some think, with respect to the blessed Seed, Christ, who was to come out of Abraham's thigh, as the phrase is, Genesis 46:26, because this rite was used only to believers.
Related Commentaries of Genesis 24:2
Genesis 24:2
2 And Abraham said unto his eldest servant of his house, that ruled over all that he had, Put, I pray thee, thy hand under my thigh: