Stephen Charnock on 2Corinthians 5.21:
By a divine statute . . . [Christ] was ordained to be put into the state and condition of a sinner in our stead;
not into the practical and experimental state of sin,
but the penal state of a sinner,
to be a sacrifice for it, not to be polluted with it.
Indeed, had not God appointed it, it had not been meritorious;
for the merit was not absolute for us,
but according to the covenant and condition;
it was capable of meriting because of the worth and dignity of the person,
but not actually meritorious for us [except on the basis of] the covenant transacted between the Father and the Son;
that it should be performed by him for us, and accepted by the Father for us, and applied by the Spirit to us.
From Christ Crucified (p. 10), originally published in 1684, four years after Charnock’s death. Minor edits added.