because he is unborn and immortal
but also because, just as he has no beginning and no end, He-Is.
He is incomprehensible in his greatness
inscrutable in his wisdom
invincible in his power
and unfathomable in his sweetness.
Truly, he alone is the good unborn and perfect Father
who is complete
who is filled with all his offspring
and with every virtue
and with everything of value...
It is not possible for mind to conceive him,
nor can words convey him,
nor can eyes see him,
nor can bodies touch him,
because of his inscrutable greatness
and incomprehensible depth
and immeasurable height
and boundless will.
This is the nature of the Unbegotten One.
Tripartite Tractate 52.35-53.11, 54.15-25 (a Valentinian creed about the Father, ca. 180-210 CE)
(translated by DeConick)