Heraclitus (flourished around 500 BCE).
Fragment 32. That which alone is wise is one; it is willing and unwilling to be called by the name of Zeus.
Fragment 2. Therefore one must follow (the universal Law, namely) that which is common (to all). But although the Law is universal, the majority live as if they had understanding peculiar to themselves.”
Fragment 119. The god (daimon, indwelling divine spirit) is home (ethos) for a human being.
Parmenides (fl. 475 BCE)
Fragment 1 narrates a mystical experience of being carried in a chariot driven by goddesses who pilot him through the Gate of Justice on the way to his insight: Being is, necessarily, and must not be thought not to be.
Socrates (469-399 BCE), hauled into court in charges of corrupting the youth by teaching unconventional things about the gods, and even being an atheist, defended himself in various ways. He told the story of the Delphic oracle, where the priestess said that he was the wisest man in Greece. He appealed to the widespread acknowledgement of his divine voice, the daimon—or divine sign (daimonion) which must come from God or the gods—so how could I be an atheist? And he said that the gods, in every way in which they ever communicate with mortals, had commanded him to try to wake up the Athenians to the pursuit of truth, beauty, and goodness rather than material attractions.
Condemned by the jury to die in prison, his friend comes to persuade him (unsuccessfully) to break the law fabric of Athens by breaking out of prison, and as Socrates wakes up to find his friend Crito there, he tells of a dream: A woman in a long, white robe assured him, “On the third day, you will come to beautiful Phithia”—which Socrates interpreted as assurance of his passage to heaven in three days. The day of his death (by drinking hemlock), he speaks with friends about reasons for belief in the immortality of soul, and after the last “proof,” finding them still fearful, he tries to calm them by telling his vision of the life after death, which, for the “philosopher” who has purified his soul by sustained pursuit of truth, beauty, and goodness, leads to glorious realms above.
Plato (427-347), a student of Socrates, continued this tradition of spirituality to some extent, but dropped the concept of an indwelling spirit presence, proposing instead that intellect/reason was the divine gift. In the dialogues he wrote, the primary interest is in rigorous philosophical understanding, but the reader repeatedly sees a secondary discourse weaving in and out, a religious, mythical, and poetic discourse, which some interpreters regard as a sop to the masses and others interpret as the only way Plato could convey his higher insights.
Aristotle (384-322), a student of Plato, affirmed in the Metaphysics 12.7 that God is the life of the thinking of eternal truth; God is in a state which is beyond even our highest experience of contemplative thinking. In the Nicomachean Ethics 10.7, he affirms that the highest happiness is the perfection of the highest within us, the intellect, which is either divine or the most divine within us, and we should do everything we can to live the divine life.
Thomas Aquinas (1225-1274), a Christian in theology and Aristotelian in philosophy, who preserved certain Platonic themes in his system, taught that we only gain knowledge by developing an intellectual understanding of what comes through the senses. Nevertheless, he indicates a certain openness to religious experience when he says that, in addition to the moral virtues such as courage, self-mastery, and prudence, and intellectual virtues such as wisdom, there are theological virtues—faith, hope, and love (caritas)—which are infused into the soul by God.
Rene Descartes (1596-1650), living when confidence in theological systems was crumbling, went in quest of an absolutely certain foundation for knowledge. He found the proposition “I think, I am” to be perfectly evident every time he would pronounce it or conceive it with perfect clarity and distinctness in his mind. In order for this criterion to be accepted as a guarantee of knowledge, however, it was necessary to prove the existence of God as the perfect Creator of the mind and of everything that the intellect can truly understand if it functions at its best. Descartes’ proof for the existence of God relies on a concept of God as “a certain substance that is infinite, independent, supremely intelligent and supremely powerful, and that created me along with everything else that exists.” He argued that this concept could not have come from any finite, limited source, and inherently implied a cause that could only be God himself. JHW proposed that Descartes was initially impressed by this proof because, as he was thinking about the idea of God, his religiously sensitive mind felt a great reality in the attributes included in the idea of God.
Immanuel Kant (1724-1804) lived at a time when many of the intellectual elite agreed that religion had disgraced itself by involvement in wars, and needed to turn to reason and turn away from mute feelings, “enthusiasm,” and fanaticism. He criticized the person who “needs neither reason nor scholarship, but merely an inner feeling, to recognize the true meaning of Scripture as well as its divine origin. Now we certainly cannot deny that “he who follows its teachings and does what it commands will surely find that it is of God,” and that the very impulse to good actions and to uprightness in the conduct of life, which the man who reads Scripture or hears it expounded must feel, cannot but convince him of its divine nature; for this impulse is but the operation of the moral law which fills man with fervent respect and hence deserves to be regarded as a divine command. A knowledge of laws, and of their morality, can scarcely be derived from any sort of feeling; still less can there be inferred or discovered from a feeling certain evidence of a direct divine influence; for the same effect can have more than one cause. In this case, however, the bare morality of the law (and the doctrine), know through reason, is the source [of the law’s validity]; and even if this origin were no more than barely possible, duty demands that it be thus construed unless we wish to open wide the gates to every kind of fanaticism, and even cause the unequivocal moral feeling to lose its dignity through affiliation with fantasy of every sort. Feeling is private to every individual and cannot be demanded of others [even] when the law, from which and according to which this feeling arises, is known in advance; therefore one cannot urge it is as a touchstone for the genuineness of a revelation, for it teaching absolutely nothing, but it merely the way in which the subject is affected as regards pleasure or displeasure-and on this basis can be established no knowledge whatever.” (Religion Within the Limits of Reason Alone p, 104-05).