John Calvin Commentary Deuteronomy 10:16

"Circumcise therefore the foreskin of your heart, and be no more stiffnecked." — Deuteronomy 10:16 (ASV)

Circumcise, therefore. From this inference it appears why mention was made of this adoption, namely, that the Jews should more earnestly and solemnly serve God, whom they knew from experience to be so gracious. He requires, then, a reciprocal love, for nothing could be more base than not to testify their gratitude by a pious and righteous life.

But, because men are by no means inclined or disposed to obey God, Moses exhorts them to self-renunciation, and to subdue and correct their carnal affections, for to circumcise the heart is equivalent to cleansing it from wicked lusts. Meanwhile, he reproves their former perverseness when he desires them to be no more stiff-necked, as if to say that now at last they should put off that depravity of mind in which they had too long hardened themselves.

We now perceive the design of Moses. He would have his fellow-Israelites submissive and obedient to God, who, by His great goodness, had provided them with the motive. But, because previously they had repaid His kindnesses with ingratitude, at the same time, he urges them to amend their conduct.

In the first clause, he alludes to the rite appointed by the Law, for circumcision is, as it were, the solemn consecration by which the children of Abraham were initiated into the worship of God and true piety, and at the same time were separated from heathen nations, to be His holy and peculiar people. They were to be admitted to this elementary rite in their infancy so that by its visible sign they might learn that the defilements of the flesh and the world were to be renounced.

There were also other objects in circumcision, but here reference is only made to newness of life, or repentance (resipiscentia). Therefore, the conclusion is that since God had chosen them as His people and by an external sign had devoted them to the cultivation of holiness, they should sincerely and really prove that they differed from heathen nations, and that they were circumcised in spirit, no less than in the flesh.

For Paul declares that only they are truly Jews who are circumcised inwardly, as he says, and not those who only have to boast of the letter of circumcision (Romans 2:28–29).

For this reason, the Prophets frequently taunt the transgressors of the Law by calling them uncircumcised, although they bore the visible sign in their flesh. In short, when he desires to exhort them to sanctify themselves to God, he reasons from the nature and use of the sign by which they professed themselves to be His chosen people. In the second clause, there is an elegant metaphor, of frequent occurrence, taken from oxen; for, since the oxen which quietly offer their necks to the yoke are easily subdued to obedience, those are said to be “stiff-necked” (durae cervicis) which are fierce and obstinate in their nature.