Vine's Expository Dictionary of NT Words
lit., "a go-between" (from mesos, "middle," and eimi, "to go"), is used in two ways in the NT, (a) "one who mediates" between two parties with a view to producing peace, as in 1 Timothy 2:5 , though more than mere "mediatorship" is in view, for the salvation of men necessitated that the Mediator should Himself posses the nature and attributes of Him towards whom He acts, and should likewise participate in the nature of those for whom He acts (sin apart); only by being possessed both of deity and humanity could He comprehend the claims of the one and the needs of the other; further, the claims and the needs could be met only by One who, Himself being proved sinless, would offer Himself an expiatory sacrifice on behalf of men; (b) "one who acts as a gurantee" so as to secure something which otherwise would not be obtained. Thus in Hebrews 8:6; 9:15; 12:24 Christ is the Surety of "the better covenant," "the new covenant," guaranteeing its terms for His people.In Galatians 3:19 Moses is spoken of as a "mediator," and the statement is made that "a mediator is not a mediator of one," Galatians 3:20 , that is, of one party. Here the contrast is between the promise given to Abraham and the giving of the Law. The Law was a covenant enacted between God and the Jewish people, requiring fulfillment by both parties. But with the promise to Abraham, all the obligations were assumed by God, which is implied in the statement, "but God is one." In the Sept., Job 9:33 , "daysman."
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Vines, W. E., M. A. Entry for 'Mediator'. Vine's Expository Dictionary of NT Words. https://www.studylight.org/dictionaries/eng/ved/m/mediator.html. 1940.