The core difference between Orthodox Fundamentalism and Orthodox Modernism manifests in their approach to traditional dogmas and spiritual life.

Orthodox Belief at a Crossroads: Tradition vs. Modern Adaptation

The core difference between Orthodox Fundamentalism and Orthodox Modernism manifests in their approach to traditional dogmas and spiritual life. Supporters of fundamentalism insist on an unconditional preservation of an untouched, “pure” faith and strict adherence to the moral and spiritual norms of the Church, whereas the modernist approach allows for compromise, adapting traditional teachings to contemporary realities and often straying from the original eschatological focus.

As illustrated by one source, modernism is characterized by the idea that “everything is possible, everything is allowed”:
"Modernism is a religion of unlimited compromise, for which everything is possible, everything is allowed. It is not the pure wine of Christ’s Truth, but wine diluted with water, as dishonest, profit-driven innkeepers do..." (source: link txt).

Another source emphasizes that modernists try to evaluate the spiritual world based on inner feelings, creating an illusory picture instead of engaging in a genuine spiritual life that demands repentance and the struggle against passions:
"We come full circle: modernists, relying on inner feelings, want to assess the world of spiritual phenomena. It is like trying to grasp human thought through touch. Instead of the spiritual world, they invent their own fantastical realm, a world of illusions. One can only truly engage with the spiritual world through repentance and the struggle against passions, by means of Orthodox mysticism." (source: link txt).

In contrast, the fundamentalist approach implies steadfastness and strictness in preserving true Orthodox traditions, where spiritual development and an inner search are of key importance, and any attempt to adapt to modernity is seen as a threat to the deep, unchanging essence of faith. This opposition is also highlighted in a critical view of modernist tendencies, describing their influence as something alien capable of corroding the ecclesiastical body from within:
"At first, this virus pretends to be 'one of our own', gradually eroding the ecclesiastical body from within, and eventually leading to a complete loss of spiritual immunity against any theories and innovations." (source: link txt).

Thus, the key differences lie in the fact that fundamentalism consistently relies on traditional, untouched doctrines and demands internal spiritual discipline, while modernism seeks to 'renew' faith in accordance with contemporary conditions—a move that, according to its critics, ultimately weakens the true spiritual value of Orthodoxy.

Supporting citation(s):
"Modernism is a religion of unlimited compromise, for which everything is possible, everything is allowed. It is not the pure wine of Christ’s Truth, but wine diluted with water, as dishonest, profit-driven innkeepers do..." (source: link txt)
"We come full circle: modernists, relying on inner feelings, want to assess the world of spiritual phenomena. It is like trying to grasp human thought through touch. Instead of the spiritual world, they invent their own fantastical realm, a world of illusions. One can only truly engage with the spiritual world through repentance and the struggle against passions, by means of Orthodox mysticism." (source: link txt)
"At first, this virus pretends to be 'one of our own', gradually eroding the ecclesiastical body from within, and eventually leading to a complete loss of spiritual immunity against any theories and innovations." (source: link txt)