The four Gospels are the pinnacle of the books of the Holy Bible since they are the words and life of our Lord Jesus Christ. All of the books of the Old Testament point to their fulfillment in our Lord Jesus Christ and the rest of the books of the New Testament are the continuation of His teachings and the work of the Holy Spirit through the words and life of our fathers, the holy apostles, and the Church.

The Church has known of only four Gospels: Matthew, Mark, Luke, and John. These are known as the true Gospels that have documented the words and life of our Lord Jesus Christ, not because the Church declared them to be, but rather because they were always known to be from the time that they were written by their respective authors as inspired by the Holy Spirit. The list of canonical books of the Bible was written by the Church afterwards only when, on the one hand, heretics like Marcion were eliminating certain books of the Bible, and on the other hand, other so-called gospels were appearing, e.g. the Gospel of Peter, the Gospel of Judas, the Gospel of Thomas, etc...

In addition to the numerous codices and manuscripts of the New Testament that contain only four gospels (Codex Sinaiticus [4th century], Codex Alexandrinus [beginning of 5th century], Codex Vaticanus [beginning of the 4 th century], Codex Ephraemi [beginning of the 5th century], Codex Bezae [4th-5th centuries], Codex Washingtonianus [5th century], and Codex Koridethianus [8th-9th centuries]) the presence of only four Gospels is well documented from the early centuries of Christianity from which we will list just some:

Muratorian Fragment
This document is named after its discoverer and first editor, L. A. Muratori (in the "Antiquitates italicae", III, Milan, 1740, 851 sq.), and is the oldest known list of books of the New Testament, dated c. 180-200 A.D. The beginning is missing; the preserved text begins with the last line concerning the second Gospel and the notices, preserved entire, concerning the third and fourth Gospels:

"...at which nevertheless he was present, and so he placed [them in his narrative]. The third book of the Gospel is that according to Luke... The fourth of the Gospels is that of John, [one] of the disciples" (Metzger, The Canon of the New Testament, Oxford University Press, 1987, p. 305-306).

Irenaeus of Lyons (120-202 A.D.)
Irenaeus documents that there are four, and only four gospels, and contemplates saying:

"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' 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 sitteth 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. As also David says, when entreating His manifestation, 'Thou that sittest between the cherubim, shine forth.' For the cherubim, too, were four faced, and their faces were images of the dispensation of the Son of God... For the living creatures are quadriform, and the Gospel is quadriform, as is also the course followed by the Lord. For this reason were four principal covenants given to the human race: one, prior to the deluge, under Adam; the second, that after the deluge, under Noah; the third, the giving of the law, under Moses; the fourth, that which renovates man, and sums up all things in itself by means of the Gospel, raising and bearing men upon its wings into the heavenly kingdom" (Adv. Haer. III, XI, 8; in Ante-Nicene Fathers, vol. 1).

Origen (c. 185-254 A.D.)
In his Commentary on the Gospel of Matthew (Ante-Nicene Fathers, vol. 10, Book I) he writes:

"Concerning the four Gospels which alone are uncontroverted in the Church of God under heaven, I have learned by tradition that the Gospel according to Matthew, who was at one time a publican and afterwards an Apostle of Jesus Christ, was written first; and that he composed it in the Hebrew tongue and published it for the converts from Judaism. The second written was that according to Mark, who wrote it according to the instruction of Peter, who, in his General Epistle, acknowledged him as a son, saying, 'The church that is in Babylon, elect together with you, saluteth you; and so doth Mark my son.' And third, was that according to Luke, the Gospel commended by Paul, which he composed for the converts from the Gentiles. Last of all, that according to John."

Eusebius of Caesarea (265-340 A.D.)
In his Ecclesiastical History (Nicene & Post-Nicene Fathers, series 2, vol. I, Book III, ch. xxv) he writes:

"Since we are dealing with this subject it is proper to sum up the writings of the New Testament which have been already mentioned. First then must be put the holy quaternion of the Gospels; following them the Acts of the Apostles...."

St. Cyril of Jerusalem (c. 350 A.D.)
In his Catechetical Lectures (Nicene & Post-Nicene Fathers, series 2, vol. VII, iv, 36) it is written:

"Then of the New Testament there are the four Gospels only, for the rest have false titles and are mischievous. The Manichaeans also wrote a Gospel according to Thomas, which being tinctured with the fragrance of the evangelic title corrupts the souls of the simple sort."

Synod of Laodicea (c. 363 A.D.)
The ancient epitome of canon 60 of this synod gives a list of New Testament books that begins:

"But of the new [testament], the four Gospels — of Matthew, of Mark, of Luke, of John..." (Nicene & Post-Nicene Fathers, series 2, vol. 14).

St. Athanasius (367 A.D.)
He writes in his 39th Festal Epistle:

"Again it is not tedious to speak of the [books] of the New Testament. These are, the four Gospels, according to Matthew, Mark, Luke, and John..." and continues after listing the entire list of New Testament books: "These are fountains of salvation, that they who thirst may be satisfied with the living words they contain. In these alone is proclaimed the doctrine of godliness. Let no man add to these, neither let him take ought from these. For concerning these the Lord put to shame the Sadducees, and said, 'Ye do err, not knowing the Scriptures.' And He reproved the Jews, saying, 'Search the Scriptures, for these are they that testify of Me'" (Nicene & Post-Nicene Fathers, series 2, vol. 4).

Apostolic Canons (c. 380 A.D.)

"...But our sacred books, that is, those of the New Covenant, are these: the four Gospels of Matthew, Mark, Luke, and John..." (from Canon 85, Apostolic Constitutions, Ante-Nicene Fathers, vol. 7 = Canon II:55 according to the Apostolic Canons' numbering in the Coptic Church).

References:
- Manuscripts of the Holy Bible in its Original Languages, Fr. Shenouda Maher Ishak
- Catholic Encyclopedia
- The Canon of the New Testament, Bruce M. Metzger
- Ante-Nicene Fathers
- Nicene & Post-Nicene Fathers

Holy Bible Interesting Fact