John of Damascus opens his Exposition of the Orthodox Faith with a citation of John 1.18, and thereby also with a programmatic statement of God’s ineffability and the corresponding need for revelation if any creature is to know him.
No one has seen God at any time; the Only-begotten Son, which is in the bosom of the Father, He has declared Him. The Deity, therefore, is ineffable and incomprehensible. For no one knows the Father, save the Son, nor the Son, save the Father. Matthew 11:27 And the Holy Spirit, too, so knows the things of God as the spirit of the man knows the things that are in him. 1 Corinthians 2:11 Moreover, after the first and blessed nature no one, not of men only, but even of supramundane powers, and the Cherubim, I say, and Seraphim themselves, has ever known God, save he to whom He revealed Himself.
If God had chosen to, he could have allowed all creatures, including the angels, to be ignorant of their maker. God is incomprehensible, and man cannot traverse the gap between his creaturely condition and the uncreated God.
But God can. And, because he willed that creatures know him, he did.
God, however, did not leave us in absolute ignorance. For the knowledge of God’s existence has been implanted by Him in all by nature. This creation, too, and its maintenance, and its government, proclaim the majesty of the Divine nature. Wisdom 13:5 Moreover, by the Law and the Prophets in former times and afterwards by His Only-begotten Son, our Lord and God and Saviour Jesus Christ, He disclosed to us the knowledge of Himself as that was possible for us. All things, therefore, that have been delivered to us by Law and Prophets and Apostles and Evangelists we receive, and know, and honour, seeking for nothing beyond these. For God, being good, is the cause of all good, subject neither to envy nor to any passion. For envy is far removed from the Divine nature, which is both passionless and only good. As knowing all things, therefore, and providing for what is profitable for each, He revealed that which it was to our profit to know; but what we were unable to bear He kept secret. With these things let us be satisfied, and let us abide by them, not removing everlasting boundaries, nor overpassing the divine tradition Proverbs 22:28 .
From this, we can see that God has done so in three ways:
After this, he might seem to add a fourth (the Apostles and Evangelists), but this is really another addition to (2): note that they are grouped together with the Law and the Prophets (“[a]ll things…that have been delivered…by Law and Prophets and Apostles and Evangelists”). The Incarnation of the Son forms the hinge between the former and the latter: as the Law and the Prophets look forward to the Son’s coming, the Apostles and Evangelists look backward to, and testify of, it.
And then the crucial addition: we are to “seek for nothing beyond these.”
So, the argument in summary form: God is incomprehensible in himself; but God wishes to be known by creatures; therefore God reveals to them whatever they needed to know; this revelation, as touching his existence, comes by nature, and, as touching his Son, is contained in the Law, Prophets, Apostles, and Evangelists; anything beyond this we could not bear, and thus should not seek.
In the realm of faith, the revelation of the Law, Prophets, Apostles, and Evangelists forms the boundaries; it is the “divine tradition.” We must be satisfied with it. If we are not, the problem is ours, not God’s. Our reliance upon and satisfaction with it, moreover, is directly predicated on the divine nature, our nature, and what must be the case if God’s will to be known and loved by creatures is to be done. It is a necessary correlate of divine infinitude and creaturely finitude. The doctrine of God, in other words, implies the necessity and sufficiency of divine revelation. And it is this that sets the stage for theological reflection. Indeed, it is this alone that makes theological reflection possible.