In the middle of the second century A.D., a Syrian Christian by the name of Tatian produced the Diatessaron (from the Greek meaning one through four). It was his attempt to create a single composite gospel by combining and harmonizing the texts of Matthew, Mark, Luke and John. This work was ultimately rejected by the Church. Indeed, St. Irenaeus, in the third book of his Against the Heresies, insists on four Gospels:
It is not possible that the Gospels can be either more or fewer in number than they are. For, since there are four zones of the world in which we live, and four principal winds, while the Church is scattered throughout all the world, and the ‘pillar and ground’ (1 Tim. 3:15) of the Church is the Gospel and the spirit of life; it is fitting that she should have four pillars, breathing out immortality on every side, and vivifying men afresh. From which fact, it is evident that the Word, the Artificer of all, He that sits upon the cherubim, and contains all things, He who was manifested to men, has given us the Gospel under four aspects, but bound together by one Spirit.
Note that last line — bound together by one Spirit. If we limit ourselves to one Gospel or attempt to harmonize the four into one, we limit God’s ability to speak to us through Scripture. Consider the following passage from the fifth chapter of the first book of St. Ambrose’s On the Holy Spirit:
The Holy Spirit, through Whom the things that are good are ministered to us, is never evil. Whence two evangelists in one and the same place, in words in differing from each other, have made the same statement, for you read in Matthew: ‘If you, being evil, know how to give good gifts to your children; how much more shall your Father, Who is in heaven, give good things to them that ask Him.’ (7:11). But according to Luke you will find it thus written: “How much more shall your heavenly Father give the Holy Spirit to them that ask Him?’ (11:13). We observe, then, that the Holy Spirit is good in the Lord’s judgment by the testimony of the evangelists, since the one has put good things in the place of the Holy Spirit, the other has named the Holy Spirit in the place of good things. If, then, the Holy Spirit is that which is good, how is He not good?
If St. Ambrose were limited to just one Gospel (harmonized or no), he would be unable to make this comparison and therefore this argument on the goodness of the Holy Spirit. This goodness is revealed by having two different voices speak about the same thing. The Spirit reveals Himself through this diversity and thus demonstrates the unity of the Gospel. In turn, this reveals the unity and diversity that exists, not only within the Church, but in the Godhead — one in essence and in three persons. Amen.