James Charlesworth writes (The Pseudepigrapha and Modern Research, pp. 123-124):
While this writing is extant in Ethiopic and Arabic (see M. R. James, The Testament of Abraham [T&S 2] Cambridge: CUP, 1892; pp. 6f., 157), the major version is the Coptic, extant in Bohairic and Sahidic. The latter dialect is the most important and was edited recently by K. H. Kuhn ("The Sahidic Version of the Testament of Isaac," JTS n.s. 8  226-39). English translations of the Arabic and both dialects of the Coptic have been published: of the Arabic by W. E. Barnes (extracts only in an appendix to James' The Testament of Abraham, pp. 140-51); of the Bohairic by S. Gaseles (in an appendix to G. H. Box's The Testament of Abraham [TED] London: S.P.C.K., 1927; pp. 57-75); and of the Sahidic by K. H. Kuhn (no. 904).
There is agreement that the Testament of Isaac, which is not mentioned in ancient lists of Old Testament apocryphal works, is dependent upon the Testament of Abraham, but the exact date is difficult to discern. P. Nagel (no. 907) thinks it was written around A.D. 400 and M. Delcor (no. 507, p. 83) affirms its earliness, suggesting because of affinities with the Dead Sea Scrolls that it may come from approximately the same milieu and date as the Testament of Abraham. Kuhn cautions, however, that there is really no convincing evidence for a precise dating of the Testament of Isaac (no. 904). Nagel (no. 907) argues that the Sahidic version, the earliest, is translated from Greek. Kuhn (no. 904) responds that Nagel's published argument is questionable.
The most intriguing question concerns the Christian elements in the text. Some of these, I am convinced, are interpolated because they are not grammatically linked to the contiguous sentences and appear to disrupt the flow of thought (viz. 14v, first sentence; from 16r, last sentence, to 17r, first sentence; 24v, second sentence; 25v, concluding statement). Other passages (e.g. 15r, third sentence) are similar to traditions in the New Testament, but it is difficult to trace the direction of influence, if any.
The Sahidic text covers 27 pages of about 80 words per page. The setting for the narrative is the events immediately before Isaac's death and the separation of his soul from the body. Isaac converses with angels, Jacob, a crowd, and a priest within the crowd, to whom he presents a series of ethical exhortations. He ascends to heaven under the guidance of 'the angel of Abraham.' He sees torments and tormentors, esepcially Abdemerouchos, who is in charge of punishments. Isaac is taken higher where he sees and worships Abraham, who receives from the Lord two conditions for becoming "a son in my kingdom." These requirements are provision for Isaac with reference for his testament, and compassionate deeds. Exceptions are allowed, by the mercy and love of the Lord, for those who cannot fulfill these requirements; the most important provision is the offering of a sacrifice in the name of Isaac. The Lord commands Michael to assemble the angels and saints before Isaac, who then sees "the face of our Lord" (epho mpencoeis). Jacob embraces his father and receives a blessing from the Lord, who then takes Isaac's soul from the body with his chariot and ascends into the heavens.
W. F. Stinespring writes: "There are pronounced Christian elements in the Testament of Isaac as it now stands, and in its present form it has the function of emphasizing the state of the deaths of Abraham and Isaac as commemorated in the Coptic Church. Thus it would be possible to see the work as springing from the Coptic Christian Church. The Christianizing is not thoroughgoing, however, and it seems more likely that the original composition was a product of Egyptian Judaism." (The Old Testament Pseudepigrapha, vol. 1, p. 904)
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