... Isaac greatly steered the doctrinal development concerning the office of Christ’s mediatorship during his lifetime, and he must be credited duly a prime mover, especially since he lived so close to the death of Theodore Beza (d. 1605). Isaac Ambrose understood Jesus’ installation to the office of the mediator to be before the foundation of the world, because of the pactum salutis, which the Father made with Him in the divine decree. He says, “there was a designation and appointment of Christ from all eternity, to the office of mediatorship: whence Christ is said to be sealed by the Father”11 (Jn. 6:27, Isa. 42:1). This was a promise from the Father to the Son, which the Father covenanted with Him.12 Christ accepted this office, for he did not take this office of mediatorship upon himself, but the Father called him to it.13 As we observed in the last chapter concerning the covenant of redemption, it was commonly held within the Reformed tradition that the office of the Mediator was likened to the doctrine of the eternal generation of the Son. “Observe how the church of God is given to Christ, as a reward of that obedience which he showed in accepting of the office of a surety for us.” According to Ambrose, the Son was given this office of surety (mediatorship) from all eternity. Isaac not only promoted the view that Christ was given the office of the Mediator primordially before the foundation of the world, but he also described the prophetic office of Christ as a mediation of revelation. “Thus Christ is a Mediator…and…by him it is that the mind and will of God is imparted to man” (John 1:18). Through Christ, God imparts his knowledge and ways to man. Christ unfolds the secrets of the Father’s bosom to us. “Christ Jesus is a Mediator, a middler an interpreter, an intermessenger betwixt God and his people.” Christ’s mediation of revelation is, according to the English divine, not only delivered to his people in his own person, but Christ delivers the message of His Father’s will “by his servants the ministers.” Ministers of the gospel are given words from the great Shepherd to mediate the knowledge of God’s truth to the people. The Mediator, through the preaching of His Word and the working of His Spirit, “opens the eyes of the mind,” to see and hear Christ speaking to the heart. However, the puritan sees an end to Christ’s mediatorial work in the new creation, he penned and dedicated a whole chapter to this idea in his work Looking Unto Jesus, which came out to 16 pages describing the cease of the office of the mediator. In Of Christ’s surrendering, and delivering up the Kingdom to God, even the Father, he piggybacks off of Calvin’s notion of the end of Christ’s priestly office, but takes it a step farther. Here, he describes the last presentation that Christ gives to the Father, the church, and the removal of the office, but from the perspective of the Son.
O my Father! See what a number I have brought home to thee; thou knowest what I have done, and what I have suffered, and what offices I have gone through to bring these hither; and now my mediatorship is done, I resign all my charge to thee again; see what a goodly troop, what a noble army I have brought thee home; why all these are mine, and “all mine are thine, and all thine are mine, and I am glorified in them, all that thou gavest me I have kept, and none of them is lost,” John. 17:10-12.23
Here, it seems that although Ambrose believed that Christ was commissioned by his Father to be a mediator from all eternity, he understands that all of the offices of mediatorship Christ took on, “what offices I have gone through to bring these hither,” were solely for a redemptive purpose, to bring the saints to God. “Thus Christ having discharged all his offices imposed upon him, now the work is finished, he leaves his function, by delivering up his commissions to his Father.”26 This motivation for the office of the Mediator is stagnated on Ambrose’s part due to his interpretation of 1st Corinthians 15:24-28. He understands that when the Son gives everything over to the Father, that God might be all in all, this must mean aspects of the office that come from Christ’s human nature.
The Arians hence inferred, that the Son was not equal with the Father, because he that is subject must needs be inferior to him whose subject he is. But the answer is easy, Christ is considered either as God, or as man, and Mediator betwixt God and man; Christ as God, hath us subject to him, and is subject to none; but Christ, as man and Mediator, is subject to his Father, together with us…Christ delivers up his kingdom as man, and as Mediator betwixt God and man: in these respects (as we have heard,) must reign no more,
at that day his mediatorship shall cease; and by consequence, in respect of his
mediatorship, or in respect of his humanity, he shall that day be subject to the Father. ....
