What are the philosophical and theological origins of the idea that humans are God or part of God's plan?

Two ideas hiding inside the question

Your question actually mixes two different family lines of thought.

• One line says God and reality are the same thing, so humans are inside God or even identical with God [1][9].
• The other line says a personal God rules the universe and guides human affairs toward a purpose, so humans are part of God's plan without being God [87][109].

It helps to know that the word "pantheism" itself is modern, possibly first used by John Toland in 1705, but the ideas behind it are much older [7].

Ancient Eastern and pagan roots

• Pantheism in its most general form is the view that God is identical with the cosmos, and nothing exists outside God [1][9].
• In Advaita Vedanta, a major school of Hindu thought, the individual self is Brahman itself, not different from ultimate reality [2].
• The Stoics regarded God as the mind of the world, with the cosmos as his body [15]. They also insisted that God must love human beings [104] and argued for divine providence from the design they saw in nature [105].
• Pantheistic ideas show up especially in Advaita Vedanta Hinduism, some Kabbalistic Judaism, Celtic spirituality, and Sufi mysticism [8].

Neoplatonism: from the One, back to the One

• Neoplatonism teaches that all reality comes from a single principle, "the One," which is both the creative source of the universe and its ultimate end [55][56].
• All people return to the One from which they came, and a soul that returns achieves union with the cosmic universal soul [57][58].
• This return to divinity had practical paths: rites called theurgy, literally "divine-working," and mystical ascent toward union [59][63].
• The system was monistic and panentheistic: the One overflows through layers of being all the way down to ordinary matter [66]. One description says Neoplatonism was "pretty pantheistic," and the distinctions between God and creation were not built into its emanation theory [67].
• Plotinus described Intellect and Soul as "the One and not the One" — they come from the One, so they are one with it in a sense, but they are not the One itself [69].
• Neoplatonism shaped later theology in many directions. Some early Christians identified the Neoplatonic One with the Christian God [60]. Meister Eckhart carried Neoplatonic ideas into Christian mysticism with his talk of a Godhead beyond the nameable God [61], and Islamic Neoplatonism adapted the First Principle to God [62].
• Modern readers still debate whether the One is equivalent to God or a transcendental object that humans return to after death [64].

The biblical root: humans as God's image

• The Jewish and Christian version of this idea starts in Genesis, where God creates humanity in his own image [32][33].
• The Hebrew phrase "in our image" can be read two ways: as humans created "as the image of God" or as created "according to the image of God" [18]. That small grammatical fork has huge consequences.
• One scholar, Janowski, calls the human being "the living statue of God," suggesting something close to identity between God and the human creature [19].
• But other evidence pushes back. The Old Testament's strong aniconism — its refusal to make images of God — strongly contradicts identifying God with humans [20]. A careful reading of Genesis says the point is not that humans are embodiments of the deity [21].
• In Second Temple Jewish thought, however, attributing the act of creation to "the image" carried a powerful implication: the image has divinity [22].
• The New Testament then applies the image to Jesus, calling him the "image of the invisible God" and describing him as simultaneously human and God [23][37].
• Paul extends this to believers: they are transformed into Christ's likeness [24], and God predestines them to be conformed to the image of his Son [25][108].
• Some modern interpreters say being human and being the image of God are inseparable [51], or that human existence itself is meant to be relationship with God [50].
• Others read the image as a job description: humans are God's representatives and agents in ruling the world [38][52], understood through the idea of divine sonship [53].

Divinization: from image to becoming like God

• Early Christian theologians developed the image idea carefully. Irenaeus taught that humans are the image of God by their created structure but only gain full likeness to God by receiving the Spirit [28]. He also said humans were formed after God's likeness and modelled by God's hands, the Son and Holy Spirit [44], and that the Fall made humans lose the likeness while keeping the image [45].
• Augustine made the imago Dei an anthropological term: humans are made in the image of the triune God in their rational or intellectual soul, yet they remain distinct from God [26][27][46].
• Later interpreters kept relocating the image. Aquinas located it in rational, intellectual creatures [47]. Luther said the original human was created good, holy, and pure as God himself [48]. Calvin placed the proper seat of the image in the soul [49].
• In Hellenistic Jewish thought, Philo, influenced by Plato [42], said the image consists of the mind or reason, described as a divine spirit breathed into the person by the Maker [41]. He said humans are created after the image, not as the image itself [40], and he equated the ideal man with the logos but stopped short of fully identifying humans with God [43].
• Later thinkers kept pushing the boundaries. Pico della Mirandola called the human a "creature of indeterminate image," without fixed identity [29]. Herder read creation in God's image as a formation process toward true humanity [30]. Pannenberg located human similarity to God in participation in God's life, achieved by giving up one's own self-centeredness [31].
• Some theologians argue that being made in God's image means humans are destined to become divine themselves [35], or that humans possess inherent divine traits [36]. Some link the image to theosis, becoming the character of God [54]. Others take a softer line: humans will never be divine on their own, but they share certain traits with God [39].

Medieval and mystical branches

• The medieval Christian thinker Eriugena argued that all divisions of the universe reduce to God, and therefore God is in all things as their very essence [11].
• The Sufi philosopher Ibn 'Arabi identified God and the universe, using a striking metaphor: the universe is the food of God and God is the food of the universe, as each swallows the other [12].
• Pantheistic feeling runs through Advaita Vedanta, some Kabbalah, Celtic spirituality, and Sufi mysticism, all of which see the divine present in all things [8].

Early modern philosophy: Spinoza and the name "pantheism"

• Baruch Spinoza used "God" to describe the unity of all substances, and he was famously called a "God-intoxicated man" [4].
• Daniel Waterland defined this pantheism in stark terms: God and the whole universe are one and the same substance, so that human souls are only "modifications of the divine substance" [5].
• Spinoza and the later Absolute idealists reasoned that a necessary, ultimate being must be all-inclusive, and therefore divine [10].
• The name for this family of views, "pantheism," may date only to 1705, but the underlying ideas are ancient and keep reappearing across the history of philosophy [7].

German idealism: the self becomes the divine

• German idealism grew out of a long process of secularization that displaced religious authority and turned the classical Greek logos into a reality accessible to human consciousness [70].
• Kant kept a place for God through practical reason: although theoretical reason cannot prove God, practical reason postulates God and the immortality of the soul as a rational faith [73]. He famously said he had to "limit knowledge to make way for faith" [74].
• Fichte centered his philosophy on the absolute "I," or self-consciousness, as the ground of all experience [71]. His radical, anti-clerical interpretation led to the Atheism Controversy of 1798–1799 [75].
• Schelling replaced Fichte's absolute subject with a monistic "Absolute" as the ground of both nature and mind [72]. For Schelling, God contains his own self-hood, and the essence of God is locked inside every creature [79][83]. Humanity is raised to spirit or personality through the incarnation of God's personality in the Christ event [79].
• Schelling also worried about pantheistic extremes. He criticized the Spinozist line of argument that makes everything "a modified God" [80] and called it "a blending of the creator and created being" [82]. His problem was the idea that God and the world are smashed into one homogeneous substance with no room for individual freedom [81]. His own thinking was shaped by Spinoza, Fichte, Franz von Baader, Jakob Böhme, and Friedrich Christoph Oetinger [84][85][86].
• Hegel described the development of ethical life as "the march of God in the world" [13]. His absolute idealism traces the self-development of "the concept" to reveal the rational structure of actuality itself [76], moving from individual mind through social and political institutions to "absolute spirit" in art, religion, and philosophy, where Spirit fully comprehends its own freedom [78].
• After Hegel, Feuerbach and Strauss transformed the study of religion into an anthropological inquiry into human self-projection: God looked less like a being above us and more like a picture of ourselves [77].
• Some pantheistic models even say God is most revealed in human culture and history [14].

The other half: humans as part of God's plan

• The theological idea of divine providence is the belief that a personal God governs the universe [87] and that everything happens under God's sovereign guidance and control [109].
• In Christian accounts, God governs through natural laws and through miracles, and divine providence also includes God responding to prayer [88][92].
• The purpose of it all, in Catholic theology, is that all creatures manifest the glory of God and that humans glorify God, serve him, and reach eternal happiness in him [99]. The early Fathers even taught that all things are created and governed with a view to humanity [106].
• After the Fall, God is described as working a plan to make redemption available to fallen humanity [116], and as predestining believers to be conformed to the image of his Son [108].
• The Bible is the cited source for this guidance and care, for example Isaiah 28:29, Psalm 91:2, and 1 Peter 5:7 [95].
• This understanding ran through history: it was held by Jews and Christians, and acknowledged by the early church, Augustine, Thomas Aquinas, Martin Luther, John Calvin, and colonial American Puritans and revival leaders [96].
• In 1776, John Witherspoon preached that God overrules all his creatures and directs all their actions to the same great purposes [97].
• Providence was also understood to work through nations and rulers. God providentially prepared the nations, and especially the Hebrew nation, for the coming of the Messiah [117][118], and he is described as ruler over the nations [119].
• Some Christian accounts say God works in human affairs through his own laws rather than through miracles, manipulating those laws for his ultimate purpose [120][121].
• The belief in a superhuman being who directs human affairs with definite purpose appears across religions, Christian and pagan alike [100]. Greek philosophy fed into it too: Socrates admitted providence [102], while Aristotle treated providence as mere opinion because his God lived wholly apart [103].
• Philosophical theodicy also ties humans to God's plan. God gives humans free will because he wants creatures who accept him freely [112], and free creatures display the same kind of liberty we attribute to God, so they are made in the image of their creator [113]. In Hick's "soul-making" theodicy, humans are transformed through suffering and virtue into God's likeness, fitted for full friendship with God [114].

Where the two streams part ways

• Mainstream Christianity draws a firm line. Humans are created by God and contain the divine image, but according to the Bible they are not divine sparks or potential gods who just need to fan their own humanness into full divinity [89].
• The same view says believers become more than creatures made in God's image — they are transformed into children of God and heirs of eternal life, but they do not become God [91].
• One Christian writer describes pantheism as an extrapolation: some people reason that if God is everywhere, then God is everything, and that step leads toward animism and pantheism [93].
• Even within the pantheism side, the meaning of "God" shifts. Pantheists agree that the universe and everything in it form a single, all-encompassing deity [6], but thinkers like Plotinus still described created things as "the One and not the One" [69], and Schelling rejected any view that simply blends creator and creature into one substance [82]. So the idea that "humans are God" has ancient and modern sources, but it has always raised the question of how far the identity goes.