The University of Heidelberg, where Zacharias Ursinus (1534–1583) was a prominent professor, seems to have been instrumental in the development of a dual concept of covenant. While it is true that Ursinus saw a duality of circumstances between the old and new covenants, this duality is still subordinate in substance to the one covenant in Jesus Christ:
“I. WHAT IS THIS COVENANT?
A covenant in general is a mutual contract, or agreement between two parties, in which the one party binds itself to the other to accomplish something upon certain conditions, giving or receiving something, which is accompanied with certain outward signs and symbols, for the purpose of ratifying in the most solemn manner the contract entered into, and for the sake of confirming it, that the engagement may be kept inviolate. From this general definition of a covenant, it is easy to perceive what we are to understand by the Covenant here spoken of, which we may define as a mutual promise and agreement, between God and men, in which God gives assurance to men that he will be merciful to them, remit their sins, grant unto them a new righteousness, the Holy Spirit, and eternal life by and for the sake of his Son, our Mediator. And, on the other side, men bind themselves to God in this covenant that they will exercise repentance and faith, or that they will receive with a true faith this great benefit which God offers, and render such obedience as will be acceptable to him. This mutual engagement between God and man is confirmed by those outward signs which we call sacraments, which are holy signs, declaring and sealing unto us God’s good will, and our thankfulness and obedience.
A testament is the last will of a testator, in which he at his death declares what disposition he wishes to be made of his goods, or possessions.
In the Scriptures, the terms Covenant and Testament are used in the same sense, for the purpose of explaining more fully and clearly the idea of this Covenant of God; for both of them refer to and express our reconciliation with God, or the mutual agreement between God and men.
This agreement, or reconciliation, is called a Covenant, because God promises to us certain blessings, and demands from us in return our obedience, employing also certain solemn ceremonies for the confirmation thereof.
It is called a Testament, because this reconciliation was made by the interposition of the death of Christ, the testator, that it might be ratified; or because Christ has obtained this reconciliation by his death, and left it unto us, as parents, at their decease, leave their possessions to their children. This reason is adduced by the apostle Paul, in his Epistle to the Hebrews, where he says: ‘For this cause he is the Mediator of the New Testament, that by means of death, they which are called might receive the promise of eternal inheritance. For where a testament is, there must also of necessity be the death of the testator. For a testament is of force, after men are dead; otherwise it is of no strength at all whilst the testator liveth.’ (Heb. 9:15, 16, 17) Whilst the testator lives he has the right to change, to take from, or to add any thing which he chooses to his will. The Hebrew word Berith, signifies only a covenant, and not a testament; whilst the Greek word which is used in the Epistle to the Hebrews, signifies both a covenant and a testament, from which it is inferred (as some suppose) that this Epistle was written not in the Hebrew, but in the Greek language.
Obj. A testament is made by the death of the testator. But God can not die. Therefore his testament is not ratified; or this reconciliation can not be called a testament. Ans. We deny the minor proposition; because God is said to have redeemed the Church with his own blood. Hence he must have died; but it was in his human nature, according to the testimony of the apostle Peter, who says of Christ the testator, who was both God and man, that he was put to death in the flesh. (1 Pet. 3:18)
II. HOW COULD THIS COVENANT BETWEEN GOD AND MAN BE MADE?
This covenant could only be made by a Mediator, as may be inferred from the fact that we, as one of the parties, were not able to satisfy God for our sins, so as to be restored to his favor. Yea, such was our miserable condition that we would not have accepted of the benefit of redemption had it been purchased by another. Then God as the other party, could not, on account of his justice, admit us into his favor without a sufficient satisfaction. We were the enemies of God, and hence there could be no way of access to him, unless by the intercession of Christ, the Mediator, as has been fully shown in the remarks which we have made upon the question–Why was a Mediator necessary? We may conclude, therefore, that this reconciliation was possible only by the satisfaction and death of Christ, the Mediator.
III. IS THIS COVENANT ONE, OR MORE?
This covenant is one in substance, but two-fold in circumstances; or it is one as it respects the general conditions upon which God enters into an engagement with us, and we with him; and it is two as it respects the conditions which are less general, or as some say, as it respects the mode of its administration.
The Covenant is one in substance. 1. Because there is but one God, one Mediator between God and man, Jesus Christ, one way of reconciliation, one faith, and one way of salvation for all who are and have been saved from the beginning. It is a great question, and one that has been much debated, whether the ancient fathers were saved in a different way from that in which we are saved, which, unless it be correctly explained, throws much obscurity and darkness around the gospel. The following passages of Scripture teach us what we are to believe in relation to this subject: ‘Jesus Christ, the same yesterday, today, and forever.’ ‘And God gave him to be Head over all things to the Church.’ ‘From whom the whole body fitly joined together,’ &c. ‘No man hath seen God at any time, the only begotten Son which is in the bosom of the Father, he hath declared him.’ ‘There is none other name under heaven given whereby we must be saved.’ ‘No one knoweth the Father but the Son, and he to whom,’ &c. ‘No one cometh to the Father but by me.’ ‘I am the Way, the Truth, and the Life ;’ he means, I am the way by which even Adam obtained salvation. ‘Many kings and prophets desired to see the things which ye see,’ &c. ‘Abraham rejoiced to see my day, and he saw it, and was glad.’ (Heb. 13:8. Eph. 1:22; 4:16. John 1:18. Acts 4:12. Matt. 11:27. John 14:6. Luke 10:24. John 8:56.) All those, therefore, who have been saved, those under the law as well as those under the gospel, had respect to Christ, who is the only Mediator, through whom alone they were reconciled to God and saved. Hence, there is but one covenant.
2. There is but one covenant, because the principal conditions, which are called the substance of the covenant, are the same before and since the incarnation of Christ; for in each testament God promises to those that repent and believe, the remission of sin; whilst men bind themselves, on the other hand, to exercise faith in God, and to repent of their sins.
But there are said to be two covenants, the old and the new, as it respects the circumstances and conditions which are less general, which constitute the form, or the mode of administration, contributing to the principal conditions, in order that the faithful, by their help, may obtain those which are general.”
– Zacharias Ursinus (1534–1583), Commentary on the Heidelberg Catechism, p. 97-99