“The work of Christ and the message which goes out from it cannot adequately be summarized in the theological outline of a single Christian teacher. From the beginning the difference between the Gospels was necessary and was not only tolerated by the church but willed in this form. Therefore in the great communities, in the first place probably in Rome, the four Gospels were collected gradually, used in readings in the liturgy and deliberately preserved.
The forms of the one ‘saving message’ of Jesus which are so different have not weakened the church on its tense way through history, but precisely through their creative multiplicity have strengthened its identity and its missionary power.
The ‘multiplicity’ of the Gospels may sometimes seem an aporia [a problematic contradiction or paradox] to us today and perplex us, but in reality–contrary to all false attempts at harmonization–they became an inexhaustible source of power, the power which created true faith, love and hope…Looking back on the history of the church which is now almost two thousand years old we must say that, thank God, the real unity of the churches does not lie in our different, indeed controversial human convictions and efforts, but in the one Lord, the ‘head,’ i.e. ‘God incarnate,’ the judge who himself took judgment upon himself, who, ‘obedient to death on the cross,’ became the redeemer of all; whose body is the church, despite all the failure, selfishness and self-righteousness of its members, because he alone can pronounce us ‘godless’ righteous. By the will of God we have the one–unique–‘good news,’ the one Gospel which stands at the beginning of the church, in sometimes very different and human forms. Yet all four Gospels proclaim solely the one Lord of the church and the one salvation brought by him.” (Martin Hengel, The Four Gospels and the One Gospel of Jesus
Christ, pp. 167-68)