Prayer is…converse with God. Though whispering, consequently, and not opening the lips, we speak in silence, yet we cry inwardly.

For God hears continually all the inward converse. So also we raise the head and lift the hands to heaven, and set the feet in motion at the closing utterance of the prayer, following the eagerness of the spirit directed towards the intellectual essence.

And endeavouring to abstract the body from the earth, along with the discourse, raising the soul aloft, winged with longing for better things, we compel it to advance to the region of holiness, magnanimously despising the chain of the flesh.

For we know right well, that the True Christian willingly passes over the whole world, as the Jews certainly did over Egypt, showing clearly, above all, that he will be as near as possible to God.

[…] The True Christian prays throughout his whole life, endeavouring by prayer to have fellowship with God.

And, briefly, having reached to this, he leaves behind him all that is of no service, as having now received the perfection of the man that acts by love.

[…] If any occasion of converse with God becomes prayer, no opportunity of access to God ought to be omitted.

[…] Those who render the most free and kingly service, which is the result of a pious mind and of knowledge, are servants and attendants of the Divinity. Each place, then, and time, in which we entertain the idea of God, is in reality sacred.

When, then, the man who chooses what is right, and is at the same time of thankful heart, makes his request in prayer, he contributes to the obtaining of it, gladly taking hold in prayer of the thing desired.

For when the Giver of good things perceives the susceptibility on our part, all good things follow at once the conception of them. Certainly in prayer the character is sifted, how it stands with respect to duty.

But if voice and expression are given us, for the sake of understanding, how can God not hear the soul itself, and the mind, since assuredly soul hears soul, and mind, mind?

Whence God does not wait for loquacious tongues, as interpreters among men, but knows absolutely the thoughts of all; and what the voice intimates to us, that our thought, which even before the creation He knew would come into our mind, speaks to God.

Prayer, then, may be uttered without the voice, by concentrating the whole spiritual nature within one expression by the mind, in un-distracted turning towards God.

Clement of Alexandria (c.150-c.215): Stromateis 7,7.