Covenant in no way implies two parties, but the contrary, i.e., in divine things; a mediator does, but there is an object of the covenant, assurance of blessing, and the circumstances of this object may require the interposition of a mediator, righteously to obtain for, qualify, and sustain them. Christ is properly the object of the Abrahamic covenant, but then, for the Church to come in, being guilty, there must be a mediator with God for that; they are brought into the covenant through a mediator, but the covenant is not made with, or properly for them.
A covenant is a disposition of God, secured by His binding or obliging Himself; this—man being a sinner—must be by the meritorious death of the Covenanter. In the case of a man's covenant, it seems to me it was conventionally brought to the same point—the authority of God being interposed, and the covenanter bound in this by the same sanction, quod nota.
Diatheke is the divine interpretation of b'rith (covenant) as to these matters, so that in the divine inquiry of it I have no need to search with anxiety for the root or meaning of b'rith (covenant) as to its ordinary human force.