Too many times, systematic conclusions are included in covenant theologies without an actual necessity in the conclusion. For example, circumcision was given to Abraham as a seal (Romans 4:11). Putting aside for now the full meaning of this text in its context, some conclude that therefore all covenants have seals and apply the term to baptism, not as an illustration to explain baptism, but as a part of their theological system to be received and believed. Some have noted that blood is spilled in connection with a covenant and conclude therefore that apart from a blood-ritual there is no covenant. Some have noted that families are included in covenants and have concluded therefore that families are a necessary feature of all covenants.
Each of these conclusions may be true. The point is simply that they are not necessarily true because the features of one covenant cannot be used to determine the features of another covenant. There is no natural necessity, inference, or proportion between things instituted, things positive, things supernatural, things covenantal. And systems built on inferences derived from covenants, which are neither natural nor necessary, will therefore contain unnecessary, and likely illegitimate, consequences. As Nehemiah Coxe said, because covenants are instituted by God and do not arise from any natural state,
“… our Knowledge and Understanding of them, must wholly depend upon Divine Revelation…seeing the nature of them is such as transcends common Principles of Reason or natural Light.”
This distinction between creation and covenant, with its methodological implications for consequences, does not deny the analogy of faith. The limitation of the details of one covenant to the institution of the covenant is not the same as the limitation of the details of one covenant to one passage of Scripture. The Word of God may speak of one covenant in many places, and they are all to be consulted and considered as constituting the final word on the matter.
~ Samuel Renihan, The Mystery of Christ