Thomas Carlyle's religious, historical and political thought has long been the subject of debate. In the 19th century, he was "an enigma" according to Ian Campbell in the Dictionary of Literary Biography, being "variously regarded as sage and impious, a moral leader, a moral desperado, a radical, a conservative, a Christian." Carlyle continues to perplex scholars in the 21st century, as Kenneth J. Fielding quipped in 2005: "A problem in writing about Carlyle and his beliefs is that people think that they know what they are."

Carlyle identified two philosophical precepts. The first, "annihilation of self (Selbsttödtung)", is derived from Novalis. The second, "Renunciation (Entsagen)", is derived from Goethe. Through Selbsttödtung (annihilation of self), liberation from self-imposed material constraints, which arise from the misguided pursuit of unfulfilling happiness and result in atheism and egoism, is achieved. With this liberation and Entsagen (renunciation, or humility) as the guiding principle of conduct, it is seen that "there is in man a HIGHER than Love of Happiness: he can do without Happiness, and instead thereof find Blessedness!" "Blessedness" refers to the serving of duty and the sense that the universe and everything in it, including humanity, is meaningful and united as one whole. Awareness of the fraternal bond of mankind brings the discovery of the "Divine Depth of Sorrow", the feeling of "an infinite Love, an infinite Pity" for one's "fellowman".

Carlyle rejected doctrines which profess to fully know the true nature of God, believing that to possess such knowledge is impossible. In an 1835 letter, he answered Faust's question, "Wer darf ihn NENNEN [Who dares name him]? I dare not, and do not", while rejecting charges of pantheism and expressing the empirical basis of his belief:

Finally assure yourself I am neither Pagan nor Turk, nor circumcised Jew, but an unfortunate Christian individual resident at Chelsea in this year of Grace; neither Pantheist nor Pottheist, nor any Theist or ist whatsoever; having the most decided contem[pt] for all manner of System-builders and Sectfounders—as far as contempt may be com[patible] with so mild a nature; feeling well beforehand (taught by long experience) that all such are and even must be wrong. By God's blessing, one has got two eyes to look with; also a mind capable of knowing, of believing: that is all the creed I will at this time insist on.

With this empirical basis, Carlyle conceived of a "new Mythus", Natural Supernaturalism. Following Kant's distinction between Reason (Vernunft) and Understanding (Verstand) in Critique of Pure Reason (1781), Carlyle held the former to be the superior faculty, allowing for insight into the transcendent. Hence, Carlyle saw all things symbols, or clothes, representing the eternal and infinite. In Sartor Resartus, he defines the "Symbol proper" as that in which there is "some embodiment and revelation of the Infinite; the Infinite is made to blend itself with the Finite, to stand visible, and as it were, attainable there." Carlyle writes: "All visible things are emblems . . . all Emblematic things are properly Clothes". Therefore, "Language is the Flesh-Garment, the Body, of Thought", and "the Universe is but one vast Symbol of God", as is "man himself". In On Heroes, Carlyle spoke of

the sacred mystery of the Universe; what Goethe calls 'the open secret.' . . . open to all, seen by almost none! That divine mystery, which lies everywhere in all Beings, 'the Divine Idea of the World,' that which lies at 'the bottom of Appearance,' as Fichte styles it; of which all Appearance . . . is but the vesture, the embodiment that renders it visible.

The "Divine Idea of the World", the belief in an eternal, omnipresent and metaphysical order which lies in the "unknown Deep" of nature, is at the core of Natural Supernaturalism.

Carlyle revered what he called the "Bible of Universal History", a "real Prophetic Manuscript" which incorporates the poetic and the factual to show the divine reality of existence. For Carlyle, "the right interpretation of Reality and History" is the highest form of poetry, and "true History" is "the only possible Epic". He imaged the "burning of a World-Phoenix" to represent the cyclical nature of civilisations as they undergo death and "Palingenesia, or Newbirth". Periods of creation and destruction do overlap, however, and before a World-Phoenix is completely reduced to ashes, there are "organic filaments, mysteriously spinning themselves", elements of regeneration amidst degeneration, such as hero-worship, literature, and the unbreakable connection between all human beings. Akin to the seasons, societies have autumns of dying faiths, winters of decadent atheism, springs of burgeoning belief and brief summers of true religion and government. Carlyle saw history since the Reformation as a process of decay culminating in the French Revolution, out of which renewal must come, "for lower than that savage Sansculottism men cannot go." Heroism is central to Carlyle's view of history. He saw individual actors as the prime movers of historical events: "The History of the world is but the Biography of great men."