Jeremiah 8:6

Wherefore it were meet exceedingly to admire the consideration of our Lawgiver, in that, when He might bring forward His illustration from among men, and when He might have spoken of Moses and Elias and John, and others like them, who took no thought; that He might touch them more to the quick, He made mention of the irrational beings. For had He spoken of those righteous men, these would have been able to say, "We are not yet become like them." But now by passing them over in silence, and bringing forward the fowls of the air, He hath cut off from them every excuse, imitating in this place also the old law. Yea, for the old covenant likewise sends to the bee, and to the ant, and to the turtle, and to the swallow. And neither is this a small sign of honor, when the same sort of things, which those animals possess by nature, those we are able to accomplish by an act of our choice.

(Verse 6.) I listened and heard: no one speaks what is good. There is no one who repents for his sin, saying: what have I done? All have turned to their own course, like a horse rushing into battle. Called to repentance, they scornfully refuse to listen: and it is not enough for them to have sinned against the Lord and spoken blasphemy, but they all rush like horses, and with fervent speed into battle, not reflecting on their sin, nor saying, what have I done? By these things we understand that either these things are said about the whole human race, because it is prone to vices, or about the time of the Savior, when all together they became useless: there was no one who did good, there was not even one (Psalm 13). Therefore, he himself cries out mystically: Save me, Lord, for the holy one has failed (Psalm 11, 1). But if these things are so, where are those who say that we are free from sin by our own will? No one, he says, speaks what is good (Matt. XI): because we will also be held accountable for idle words on the day of judgment.

Jeremiah also says, in like manner: "The turtle and the swallow have known her time, and the sparrows of the field have observed the times of their coming, but my people have not known the judgment of the Lord. How do you say, We are wise, and the law of the Lord is with us? The meting out is in vain. The scribes are deceived and confounded. The wise men are dismayed and taken, for they have rejected the word of the Lord." Therefore (as I had begun to say), when God had determined to send to people a teacher of righteousness, he commanded him to be born again a second time in the flesh and to be made in the likeness of humankind himself, to whom he was about to be a guide, and companion and teacher. But since God is kind and merciful to his people, he sent him to those very persons whom he hated, that he might not close the way of salvation against them forever but might give them a free opportunity of following God, that they might both gain the reward of life if they should follow him (which many of them do and have done) and incur the penalty of death by their fault if they should reject their King.