But Paul's moral teaching was by no means merely an echo or reminiscence of the ethics of Jesus; it was organically connected with his own doctrinal teaching. In Paul's letters there is usually an ethical section, but this is preceded by a didactic or doctrinal section. Doctrine with him, in the words of Phillips Brooks, was the "child of faith and the mother of duty." Admittedly his doctrine is used to enforce and to inspire his ethics. A high Christology--"Christ also pleased not himself" (Rom. xv. 3)--enforces the appeal not to please oneself. The Incarnation is the supreme example of generosity to the poor, and the death upon the Cross of lowliness of mind and obedience (2 Cor. viii. 9; Phil. ii. 5-8). His own sacrifice for our sins grounds the plea for a life of unselfishness (2 Cor. v. 14, 15; Rom. xii. 1). We should walk in love as Christ loved us and gave Himself for us (Eph. v. 2); and should walk in newness of life, as Christ was raised from the dead by the glory of the Father (Rom. vi. 4). Doctrine with Paul and ethics in its solemn sanctions and its inspiring motivation are inextricably intertwined. Paul's doctrine about the person of Christ and His death and resurrection can be disentangled from his ethical teaching as little as it can from his experience. Certainly the doctrine was no alien or extraneous element in Paul's system, and certainly it strengthened rather than weakened his ethical appeal. Is there a similar blending of ethics and doctrine in the teaching of Jesus? For the gospel of Jesus in its purity we must, according to a popular school of criticism, go back of the Fourth Gospel to the Synoptics, and back of these to their sources, practically to Mark and to the source called Q (Quelle), or the Logia, representing the non-Markan agreements of Matthew and Luke. Even in these sources, it is often maintained, caution must be used, and foreign elements must be eliminated. Let us see, then, whether there is such a mingling of the ethical and the Christological in the authentic teaching of Jesus as we have noticed in that of Paul. The Sermon on the Mount, the words to the disciples after the confession of Peter (Mark viii. 34-38), and the teaching on true greatness (Mark x. 42-45), may be taken as typical examples of Jesus' ethical teaching. In these passages are not merely disconnected maxims, but an ethical system, containing a profound and, as we may say, fully thought out philosophy of life, in which the religious and ethical elements are organically united.