Gregory of Nazianzus

There have been in the whole period of the duration of the world two conspicuous changes of people’s lives, which are also called two Testaments, or, on account of the wide fame of the matter, two earthquakes; the one from idols to the law, the other from the law to the gospel. And we are taught in the Gospel of a third earthquake, namely, from this earth to that which cannot be shaken or moved. Now the two Testaments are alike in this respect, that the change was not made on a sudden or at the first movement of the endeavor. Why not (for this is a point on which we must have information)? That no violence might be done to us but that we might be moved by persuasion. For nothing that is involuntary is durable; like streams or trees that are kept back by force. But that which is voluntary is more durable and safe. The former is due to one who uses force, the latter is ours; the one is due to the gentleness of God, the other to a tyrannical authority. Therefore God did not think it behooved him to benefit the unwilling but to do good to the willing. And therefore like a tutor or physician he partly removes and partly condones ancestral habits, conceding some little of what tended to pleasure, just as doctors do with their patients, that their medicine may be taken, being artfully blended with what is nice. For it is no very easy matter to change from those habits that custom and use have made honorable. For instance, the first cut off the idol but left the sacrifices; the second, while it destroyed the sacrifices did not forbid circumcision. Then, when once men had submitted to the curtailment, they also yielded that which had been conceded to them; in the first instance the sacrifices, in the second circumcision; and became instead of Gentiles, Jews, and instead of Jews, Christians, being beguiled into the gospel by gradual changes. Paul is a proof of this; for having at one time administered circumcision and submitted to legal purification, he advanced till he could say, and I, brothers, if I yet preach circumcision, why do I yet suffer persecution? His former conduct belonged to the temporary dispensation, his latter to maturity.