Christ's taking on him to do the righteousness of the law. Nor can
the law object against the equity of this dispensation of heaven;
for why might not that God who gave the law its being and its
sanction, dispose as he pleases of the righteousness which it
commends? Besides, if men be made righteous, they are so; and if by
a righteousness which the law commends, how can fault be found with
them by the law? Nay, it is "witnessed by the law and the prophets,"
who consent that it should be "unto all and upon all them that
believe," for their justification. Rom. 3:20,21.

And that the mighty God suffereth the prince of the devils to do
with the law what he can against this most wholesome and godly
doctrine, it is to show the truth, goodness, and permanency thereof;
for this is as if it were said, Devil, do thy worst.

When the law is in the hand of an easy pleader, though the cause
that he pleads be good, a crafty opposer may overthrow the right;
but here is the salvation of the children in debate, whether it can
stand with law and justice: the opposer of this is the devil, his
argument against it is the law; he that defends the doctrine is
Christ the advocate, who in his plea must justify the justice of
God, defend the holiness of the law, and save the sinner from all
the arguments, pleas, stops, and demurs that Satan is able to put in
against it. And this he must do fairly, righteously, simply,
pleading the voice of the self-same law for the justification of the
soul that he standeth for, which Satan leads against it; for though
it is by the new law that our salvation comes, yet by the old law is
the new law approved of, and the way of salvation thereby consented
to.