Unwritten Apostolic tradition has been handed down

Now that the Savior has taught the apostles, the unwritten rendering of the written [Scripture] has been handed down also to us, inscribed by the power of God on hearts new, according to the renovation of the book.

Clement of Alexandria
The Stromata, Book VI
Chapter XV

Prophecy is obscure unless sought in love

But prophecy does not employ figurative forms in the expressions for the sake of beauty of diction. But from the fact that truth appertains not to all, it is veiled in manifold ways, causing the light to arise only on those who are initiated into knowledge, who seek the truth through love.

Clement of Alexandria
The Stromata, Book VI
Chapter XV

God gave both the Hebrew covenants and Greek philosophy

And further, that the same God that furnished both the Covenants was the giver of Greek philosophy to the Greeks, by which the Almighty is glorified among the Greeks, he shows.

…But as the proclamation [of the Gospel] has come now at the fit time, so also at the fit time were the Law and the Prophets given to the Barbarians, and Philosophy to the Greeks, to fit their ears for the Gospel.

Clement of Alexandria
The Stromata, Book VI
Chapter V & VI

The soul is temporarily separated from body before the resurrection

And if we live throughout holily and righteously, we are happy here, and shall be happier after our departure hence; not possessing happiness for a time, but enabled to rest in eternity.

Clement of Alexandria
The Stromata, Book V
Chapter XIV

The Greeks had vague references to the Trinity

For I pass over Plato; he plainly, in the Epistle to Erastus and Coriscus, is seen to exhibit the Father and Son somehow or other from the Hebrew Scriptures, exhorting in these words: “In invoking by oath, with not illiterate gravity, and with culture, the sister of gravity, God the author of all, and invoking Him by oath as the Lord, the Father of the Leader, and author; whom if ye study with a truly philosophical spirit, ye shall know.” And the address in the Timœus calls the creator, Father, speaking thus: “Ye gods of gods, of whom I am Father; and the Creator of your works.” So that when he says, “Around the king of all, all things are, and because of Him are all things; and he [or that] is the cause of all good things; and around the second are the things second in order; and around the third, the third,” I understand nothing else than the Holy Trinity to be meant; for the third is the Holy Spirit, and the Son is the second, by whom all things were made according to the will of the Father.

Clement of Alexandria
The Stromata, Book V
Chapter XIV