Doctrines are not always evident in the scriptures

Where do you find in the Old Testament or in the Gospel the Trinity, or consubstantiality, or one Godhead, or three persons, or the one substance of Christ, or His two natures, expressed in so many words? Still, as they are contained in what Scripture does say, and defined by the holy fathers, we receive them and anathematise those who do not.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part III

There are many unwritten traditions that are handed down

The eye-witnesses and ministers of the word handed down the teaching of the Church, not only by writing, but also by unwritten tradition. Whence comes our knowledge of the sacred spot, Mount Calvary, of the holy sepulchre? Has it not been handed down to us from father to son? It is written that our Lord was crucified on Calvary, and buried in the tomb which Joseph hewed out of the rock, but it is unwritten tradition that teaches us we are adoring the right places, and many other things of the same kind. Why do we believe in three baptisms, that is, in three immersions? Why do we adore the Cross? Is it not through tradition? Therefore the holy apostle says: “Brethren, stand fast; and hold the traditions which you have learned, whether by word, or by our epistle.” (II Thess. 2.15) Many things, therefore, being handed down to the Church by unwritten tradition and kept up to the present day, why do you speak slightingly of images?

I am not to be persuaded that the Church is set in order by imperial edicts, but by patristic traditions, written and unwritten. As the written Gospel has been preached in the whole world, so has it been an unwritten tradition in the whole world to represent in image Christ, the incarnate God, and the saints, to adore the Cross, and to pray towards the east.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part II

Fidelity to Church tradition, even in the slightest thing, is critical

We are obedient to you, O King, in things concerning our daily life, in tributes, taxes, and payments, which are your due; but in ecclesiastical government we have our pastors, preachers of the word, and exponents of ecclesiastical law. We do not change the boundaries marked out by our fathers (Prov. 22.28): we keep the tradition we have received. If we begin to lay down the law to the Church, even in the smallest thing, the whole edifice will fall to the ground in no short time.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part II

Epiphanius is falsely attributed to rejecting icons

If, again, you object that the great Epiphanius thoroughly rejected images, I would say in the first place the work in question is fictitious and unauthentic. It bears the name of some one who did not write it, which used to be commonly done. Secondly, we know that blessed Athanasius objected to the bodies of saints being put into chests, and that he preferred their burial in the ground, wishing to set at nought the strange custom of the Egyptians, who did not bury their dead under ground, but set them upon beds and couches. Thus, supposing that he really wrote this work, the great Epiphanius, wishing to correct something of the same kind, ordered that images should not be used. The proof that he did not object to images, is to be found in his own church, which is adorned with images to this day. Thirdly, the exception is not a law to the Church, neither does one swallow make summer, as it seems to Gregory the theologian, and to the truth. Neither can one expression overturn the tradition of the whole Church which is spread throughout the world.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I

Unwritten traditions are handed down in the Church

How do we know the Holy place of Calvary, or the Holy Sepulchre? Does it not rest on a tradition handed down from father to son? It is written that our Lord was crucified on Calvary, and buried in a tomb, which Joseph hewed out of the rock; (Mt. 27.60) but it is unwritten tradition which identifies these spots, and does more things of the same kind. Whence come the three immersions at baptism, praying with face turned towards the east, and the tradition of the mysteries?* Hence St Paul says, “Therefore, brethren, stand fast, and hold the traditions which you have learned either by word, or by our epistle.” (II Thess. 2.15) As, then, so much has been handed down in the Church, and is observed down to the present day, why disparage images?

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I

Church tradition is a faith we carry forward by imitation

A small thing is not small when it leads to something great, nor indeed is it a thing of no matter to give up the ancient tradition of the Church held by our forefathers, whose conduct we should observe, and whose faith we should imitate.

St. John Damascene
Apology Against Those Who Decry Holy Images
Part I

 

Some works were known but not included as “ecclesiastical books”

The term ἀσώματον, i.e., incorporeal, is disused and unknown, not only in many other writings, but also in our own Scriptures.  And if any one should quote it to us out of the little treatise entitled The Doctrine of Peter, in which the Saviour seems to say to His disciples, “I am not an incorporeal demon,” I have to reply, in the first place, that that work is not included among ecclesiastical books; for we can show that it was not composed either by Peter or by any other person inspired by the Spirit of God.

Origen
On First Principles, Book I
Preface

Apostolic tradition “alone” is the source of authority

…as the teaching of the Church, transmitted in orderly succession from the Apostles, and remaining in the Churches to the present day, is still preserved, that alone is to be accepted as truth which differs in no respect from ecclesiastical and apostolical tradition.

Origen
On First Principles, Book I
Preface