Biblical and Rabbinical Oath

The Gemora (Kesuvos 88a) had stated: Rav Papa said (regarding the case where there is one witness testifying that the woman collected her kesuvah): A wise husband could bring his wife to take a Biblical oath with the following method: He pays her the kesuvah (a second time) in front of another witness (and now, if se will deny receiving the kesuvah, there will be two witnesses against her) and he claims that the first monies that he paid her were actually a loan (and if she denies the loan, there will be one witness testifying against her; she will be Biblically obligated to take an oath; this will be a case of taking an oath in order to retain the money and it will be a case which doesn’t involve a lien on land)!

The Raavad explains: Even if there is no severity in the Biblical oath more than the Rabbinical one, it is still regarded as advantageous for the husband to force her to be subject to a Biblical oath besides a Rabbinical one.

Rashi explains that there is a halachic severity in taking a Biblical oath. One is required to use the Name of God and hold a Torah scroll when he takes a Biblical oath; a Rabbinical oath does not have this stringency.

Tosfos points out that Rashi himself maintains that a Rabbinical oath of our Mishna is of the same severity as a Biblical oath; it is only an oath instituted by the Amoraim that is treated leniently.

The Rishonim discuss at great length other differences between the two oaths.