39 Grk “this is my blood of the covenant that is poured out for many.” In order to avoid confusion about which is poured out, the translation supplies “blood” twice so that the following phrase clearly modifies “blood,” not “covenant.”
40 Most (A f1, 13 𝔐 lat sy) have καινῆς (kainēs, “new”) before διαθήκης (diathēkēs, “covenant”), a reading that is almost surely influenced by the parallel passage in Luke 22:20. Further, the construction τὸ τῆς καινῆς διαθήκης (to tēs kainēs diathēkēs), in which the resumptive article τό (referring back to τὸ αἶμα [to haima, “the blood“]) is immediately followed by the genitive article, is nowhere else used in Mark except for constructions involving a genitive of relationship (cf. Mark 2:14; 3:17, 18; 16:1). Thus, on both transcriptional and intrinsic grounds, this reading looks to be a later addition (which may have derived from τὸ τῆς διαθήκης of D* W 2427). The most reliable , along with several others (א B C Dc L Θ Ψ 565), lack καινῆς. This reading is strongly preferred. Jesus’ death established the forgiveness promised in the new covenant of Jer 31:31. Jesus is reinterpreting the symbolism of the Passover meal, indicating the presence of a new era.

In other versions

And he said to them, “This is my blood of the covenant, which is poured out for many.

“This is my blood of the covenant, which is poured out for many,” he said to them.

He said to them, “This is my blood of the covenant, which is poured out for many.

And he said to them, “This is my blood, which confirms the covenant between God and his people. It is poured out as a sacrifice for many.

And he said to them, “This is my blood of the covenant which is poured out for many.

And he said unto them, This is my blood of the new testament, which is shed for many.

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