Matthew Poole and continuators on 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 :

viz. Eliezer, Gen. 15. 2.

A ceremony used in swearing as now, so antiently in the Eastern parts, as Gen. 47. 29. Either as a testimony of subjection, and promise of faithful service, for this rite was used onely by inferiours towards superiours; or, as some think, with respect to the blessed seed, Christ, who was to come out of Abrahams thigh, as the phrase is Gen. 46. 26. because this rite was used onely to Believers.

Marginal references: chap. 47. 29.