I speak after the manner of men. — The figure that I am going to use is one taken from the ordinary civil relations between man and man, and therefore, it is left to be inferred, supplies an à fortiori argument in things relating to God, for men may change and break the most solemn engagements; God is absolutely faithful and unchangeable. The phrase translated “I speak after the manner of men” is found in the same, or a very similar form, in Romans 3:5; Romans 6:19; 1 Corinthians 9:8, where see the Notes.
Though it be but a man’s covenant. — This is well rendered in the Authorised version. A covenant, even though it is only between two men — though it is regulated by the provisions only of human law — does not admit of alteration or addition after it has once been signed and sealed; much more a covenant which depends on God.
Covenant. — The word thus translated is that which gave its name to the “Old and New Testaments,” where a more correct rendering would be the “Old and New Covenants.” The word has both senses. It meant originally a “disposition” or “settlement,” and hence came, on the one hand, to be confined to a “testamentary disposition,” while, on the other hand, it was taken to mean a settlement arrived at by agreement between two parties. The first sense is that most commonly found in classical writers; the second is used almost entirely in the LXX. and New Testament. The one exception is in Hebrews 9:15-17, where the idea of “covenant” glides into that of “testament,” the argument rather turning upon the double meaning of the word.
Addeth thereto. — Adds new clauses or conditions. Such new clauses could only be added by a second covenant. The reason why the Apostle introduces this point is that the Law might be supposed to restrict the bearings of the promise. It might be thought to add certain new and limiting conditions, without compliance with which the blessings of the promise could not be obtained. This was the position of the Judaising party, against which St. Paul is arguing.