Immanuel Kant, (German), is widely credited as the key player in the development of modern philosophy, and Western thought. Kant redefined the fundamentals of philosophical inquiry. Kant argued that “pure reason” could not prove God’s existence, but “practical reason” could. Kant claimed that by observing the moral instincts of people we can see that there is some kind of source beyond the mere human will itself that directs life.
We have no other rule of our actions but the conduct of that divine man within us, with which we compare ourselves, and by which we judge and better ourselves, though we can never reach it.
Immanuel Kant (F. Max Mueller) (1922). Immanuel Kant’s Critique of pure reason, London: Macmillan & Co., Ltd. p. 460 - 461
Such an ideal person, authorized to sit as JUDGE in the court of conscience, must be A SEARCHER OF THE HEART, for the tribunal is erected in the interior of man. Further, he must hold ALL-OBLIGATORY POWER, i.e., be such a person, or at least be figured as if he were a person, in respect of whom all duty may be represented as his commandments, because conscience is judge over all free actions. Lastly, he must have all power (in heaven and in earth) to absolve and to condemn, these properties being of the very essence of the functions of a judge: apart from his being endowed wherewith, he could give no effect to the law. But since he who searches the heart, and, having all-obligatory power, is able to absolve and condemn, is called GOD, it follows that conscience must be regarded as a subjective principle implanted in the reason of man, calling for an account of every action before God. Nay, THIS NOTION OF RESPONSIBILITY IS at all times involved, however darkly, IN EVERY ACT OF MORAL SELF-CONSCIOUSNESS.
This is not by any means to say that man is entitled, and still less that he is bound, to believe in, As REAL, any such Supreme Being, answering to the idea, to which conscience inevitably points; for the idea is given him not objectively by speculative reason, but subjectively only, by practical reason obliging itself to act conformably to this representation. And mankind is, by means of this idea, but merely from its ANALOGY to that of a sovereign lawgiver of the universe, led to figure to himself CONSCIENTIOUSNESS, as a responsibility owed to A MOST HOLY BEING, different from ourselves, and yet most intimately present to our substance (moral legislative reason), and to submit ourselves to His will as if it were a law of righteousness. THE NOTION OF RELIGION in genere is therefore just this, that it IS A PRINCIPLE OF ESTEEMING OF ALL OUR DUTIES AS IF THEY WERE DIVINE COMMANDMENTS.
Immanuel Kant (J. W. Semple) (1871). The metaphysic of ethics, Edinburgh: T. & T. Clark pp. 255-256
God’s existence - Besides, the cardinal truth, ‘there is a God,’ is so obvious to the eye of sane reason, and the practical belief in Him so naturally crowns all morality, as not to leave a cultivated and virtuous mind a moment in doubt of this indispensable basis, this first principle, of all true religion.
Immanuel Kant, (John Richardson) (1836). Metaphysical works of the celebrated Immanuel Kant London: Printed for W. Simpkin and R. Marshall, Stationers’ Court. p. 158