A. The eternal will of the Father to redeem the elect through Christ's suffering, and the will of the Son to offer Himself as the Surety for the elect.
In Nicholas Greendyk's exposition of the catechism, An Explanation of Rev. A. Hellenbroek's Catechism "A Specimen of Divine Truths," pp. 137-138, he first quotes from Herman Witsius' Economy of the Covenants to define this Counsel of Peace, or Covenant of Redemption as it is also called, the special covenant or transaction between Father and Son to effect the salvation of his people.
Herman Witsius, Economy of the Covenants, Vol. 1, pp. 165-166:
II. When I speak of the compact between the Father and the Son, I thereby understand the will of the Father, giving the Son to be the Head and Redeemer of the elect; and the will of the Son, presenting himself as a Sponsor or Surety for them; in all which the nature of a compact and agreement consists. The scriptures represent the Father, in the economy of our salvation, as demanding the obedience of the Son even unto death; and upon condition of that obedience, promising him in his turn that name which is above every name, even that he should be the head of the elect in glory: but the Son, as presenting himself to do the will of the Father, acquiescing in that promise, and in fine, requiring, by virtue of the compact, the kingdom and glory promised to him.
Then Greendyk goes on to quote Isaac Ambrose' intriguing exposition of Isaiah 49, which reveals in dialogue form this Counsel of Peace between Father and Son. I will quote a portion that extracted by Greendyk as well as a little more by Ambrose.
Isaac Ambrose, Looking Unto Jesus, pp. 54-55:
The covenant concerning man's salvation is the last and main particular I instanced in: I dare not be too curious to insist on the order of nature, and the rather, because I believe the covenant betwixt God and Christ from everlasting, is interwoven with the decree, foreknowledge, and election above. So the apostle tells us, "He hath chosen us in Christ before the foundation of the world," Eph. 1:4. Mark that, in Christ. There was an eternal plot betwixt the Father and the Son; there was a bargain made (I speak it with reverence) betwixt God and Christ, there was a covenant betwixt the Lord and his Son Jesus Christ, for the salvation of the elect; and of this observe we especially in these following texts.
In Isaiah 49:1,2,3,4. The prophet seems to set it dialogue-ways; one expresseth it thus: First, Christ begins, and shows his commission, telling God how he had called him, and fitted him for the work of redemption, and he would know what reward he should have of him for so great an undertaking. "The Lord hath called me from the womb, from the bowels of my mother hath he made mention of my name, and he hath made my mouth like a sharp sword, in the shadow of his hand hath he hid me, and made me a polished shaft, in his quiver hath he hid me," Isa. 49:1,2. Upon this, God answers him, and tells him what reward he should have for so great an undertaking; only at first he offers low, viz: only the elect people of Israel. And he said unto me, "Thou art my servant, O Israel, in whom I will be glorified: Or, Israel it is in whom I will be glorified by thee," Isa. 49:3. Christ who stood now a making his bargain with him, thought these too few, and not worth so great a labor and work, because few of the Jews would come in, but would refuse him, and therefore he says, he should labor in vain, if this were all his recompense, "Then said I, I have labored in vain, I have spent my strength for nought, and in vain," Isa. 49:4. And yet withal he tells God, that seeing his heart was so much in saving sinners, he would do it howsoever for these few, comforting himself with this, that his work or his reward was with the Lord. Upon this God comes off more freely, and opens his heart more largely to him, as meaning more amply to content him for his pains in dying. "It is a light thing that thou shouldest be my servant, to raise up the tribes of Jacob, and to restore the preserved of Israel," Isa. 49:6. That is not worth dying for, I value thy sufferings more than so, "I will also give thee for a light to the gentiles, that thou mayest be my salvation unto the ends of the earth." Methinks I imagine as if I heard God speak unto Christ from eternity, "See, here I have loved a remnant of mankind both of Jews and gentiles, with an everlasting love, I know they will sin and corrupt themselves, and so become enemies to me, and liable unto eternal death; now thou art a mighty person, able to do what I require of thee for them; if thou wilt take upon thee their nature and sins, and undertake to satisfy my justice and law, and make them a believing holy people, then I will pardon them, and adopt them in thee for my sons and daughters, and make them co-heirs with thee, of an incorruptible crown of life." And then Christ said, "Lo I come, to do thy will, O God," Heb. 10:7,9. Then Christ as it were, struck hands with God, to take upon him the nature and sin of man, and to do and suffer for him whatsoever God required of him. Certainly thus was the whole business of our salvation first transacted betwixt God the Father and Christ, before it was revealed to us. Hence we are said to be given unto Christ. "I have manifested thy name (saith Christ) unto the men which thou gavest me out of the world: thine they were, and thou gavest them me," John 17:6. This very giving implies, as if the Father in his eternity should have said to the Son, "These I take to be vessels of mercy, and these thou shalt bring unto me, for they will destroy themselves, but thou shalt save them out of their lost estate." And then the Son takes them at his Father's hand, and looking at his Father's will, "This is the Father's will which hath sent me, that of all which he hath given me I should lose nothing," John 6:39. He thereupon takes care of each, he would not for a world any of them should be lost, which his Father hath given him, they are more dear than so.
In Isaiah 42:1.6, this very covenant is expressly mentioned. Thus God speaks of Christ. "Behold my servant whom I uphold, mine elect in whom my soul delighteth: -- I will give thee for a covenant of the people, for a light of the gentiles," Isa. 53:11. Psalm 40:6. Yea, this covenant and agreement seems to be confirmed with an oath, in Heb. 7:28. And for this service Christ is required to "ask of God and he will give him the heathen for his inheritance," Psalm 2:8. 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. This stipulation some make to be that counsel of peace spoken of by the prophet, "And the counsel of peace shall be betwixt them both," Zech. 6:13. (i.e.) between the Lord, "and the man whose name is the Branch," verse 12. And for this agreement it is that Christ is called the second Adam; for as with the first Adam God plighted a covenant concerning him and his posterity, so also he did indent with Christ and his seed concerning eternal life to be obtained by him.