2 I do not think that I need spend much time in endeavoring to persuade you that we are Christian men; and if Christians, by virtue of the name, belonging to Christ. Upon the forehead we bear His sign; and we do not blush because of it, if we also bear it in the heart. His sign is His humility. By a star the Magi knew Him; and this sign was given by the Lord, and it was heavenly and beautiful. He did not desire that a star should be His sign on the forehead of the faithful, but His cross.
By it humbled, by it also glorified; by it He raised the humble, even by that to which He, when humbled, descended. We belong, then, to the gospel, we belong to the New Testament. “The law was given by Moses, but grace and truth came by Jesus Christ.” We ask the apostle, and he says to us, since we are not under the law but under grace. “He sent therefore His Son, made of a woman, made under the law, that He might redeem those who were under the law, that we might receive the adoption of sons.” Behold, for this end Christ came, that He might redeem those who were under the law; that now we may not be under the law, but under grace.
Who, then, gave the law? He gave the law who gave likewise grace; but the law He sent by a servant, with grace He Himself came down. And in what manner were men made under the law? By not fulfilling the law. For he who fulfills the law is not under the law, but with the law; but he who is under the law is not raised up, but pressed down by the law. All men, therefore, being placed under the law, are by the law made guilty; and for this purpose it is over their head, that it may show sins, not take them away.
The law then commands, the Giver of the law shows pity in that which the law commands. Men, endeavoring by their own strength to fulfill that which the law commands, fell by their own rash and headstrong presumption; and not with the law, but under the law, became guilty: and since by their own strength they were unable to fulfill the law, and had become guilty under the law, they implored the aid of the Deliverer; and the guilt which the law brought caused sickness to the proud. The sickness of the proud became the confession of the humble. Now the sick confess that they are sick; let the physician come to heal the sick.
Source: Tractates on the Gospel of John (New Advent)