"[...]since the first principle of everything is difficult to find out, the absolutely first and oldest principle, which is the cause of all other things being and having been, is difficult to exhibit."

"This discourse respecting God (περὶ θεοῦ λόγος) is most difficult to handle. For since the first principle (ἀρχὴ παντὸς) of everything is difficult to find out, the absolutely first and oldest principle (πάντως που ἡ πρώτη καὶ πρεσβυτάτη ἀρχὴ), which is the cause of all other things being and having been, is difficult to exhibit. For how can that be expressed (ῥητὸν) which is neither genus (γένος), nor difference (διαφορὰ), nor species (εἶδος), nor individual (ἄτομον), nor number; nay more, is neither an event (συμβεβηκός τι), nor that to which an event happens (συμβέβηκέν τι)? No one can rightly express Him wholly. For on account of His greatness (μεγέθει) He is ranked as the All, and is the Father of the universe (τῶν ὅλων πατήρ). Nor are any parts to be predicated of Him. For the One is indivisible (ἀδιαίρετον γὰρ τὸ ἕν); wherefore also it is infinite (ἄπειρον), not considered with reference to inexhaustability (ἀδιεξίτητον), but with reference to its being without dimensions (ἀδιάστατον), and not having a limit (μὴ ἔχον πέρας). And therefore it is without form (ἀσχημάτιστον) and name (ἀνωνόμαστον). [...] It remains that we understand, then, the Unknown (ἄγνωστον), by divine grace, and by the word alone that proceeds from Him; as Luke in the Acts of the Apostles relates that Paul said, “Men of Athens, I perceive that in all things ye are too superstitious. For in walking about, and beholding the objects of your worship, I found an altar on which was inscribed, To the Unknown God. Whom therefore ye ignorantly worship, Him declare I unto you.”" (Clement of Alexandria, Str. 5.12.81-82)