The Baha’i principle of oneness applies to several aspects of reality: the oneness of God, the oneness of religion, and the oneness of humanity.
The Baha’i teachings say that all of creation is a reflection of that same principle of oneness. God created all of existence, so it is natural that religious truth and scientific truth should harmonize.
Baha’u’llah upholds the importance of religion:
Religion is verily the chief instrument for the establishment of order in the world and of tranquillity amongst its peoples …. The greater the decline of religion, the more grievous the waywardness of the ungodly. This cannot but lead in the end to chaos and confusion. – Tablets of Baha’u’llah, pp. 63-64.
In truth, religion is a radiant light and an impregnable stronghold for the protection and welfare of the peoples of the world. – Ibid., p. 125.
As the body of man needeth a garment to clothe it, so the body of mankind must needs be adorned with the mantle of justice and wisdom. Its robe is the Revelation vouchsafed unto it by God. – Gleanings from the Writings of Baha’u’llah, p. 81.
He has written extensively about the positive effect of religion in past societies and civilizations. But Baha’u’llah lamented the gradual decline of religion in his own day, which he predicted would continue for some time into the future:
The face of the world hath altered. The way of God and the religion of God have ceased to be of any worth in the eyes of men … The vitality of men’s belief in God is dying out in every land …. The corrosion of ungodliness is eating into the vitals of human society. – Baha’u’llah, quoted by Shoghi Effendi in The Promised Day is Come, p. 275.
In other passages Baha’u’llah explained that religion and belief in God are indispensable prerequisites not only for individual salvation but also for true civilization—yet he also acknowledged that tremendous cruelties and suffering have been inflicted on humanity in the name of religion. He warned humanity about the importance of eliminating religious prejudice when he wrote “Religious fanaticism and hatred are a world-devouring fire, whose violence none can quench.” – Gleanings from the Writings of Baha’u’llah, p. 288. He commanded his own followers to “Consort with all men . . . in a spirit of friendliness and fellowship.” – Epistle to the Son of the Wolf, p. 15.
Abdu’l-Baha also noted the prevalence of religious intolerance, saying that it violates the spirit of true religion:
Divine religion is not a cause for discord and disagreement. If religion becomes the source of antagonism and strife, the absence of religion is to be preferred. Religion is meant to be the quickening life of the body politic; if it be the cause of death to humanity, its nonexistence would be a blessing and benefit to man. – The Promulgation of Universal Peace, p. 117.
He attributes the decline of religion in large part to the endless disputes between the followers of different faiths:
. . . materialists are advancing and aggressive while divine forces are waning and vanishing. Irreligion has conquered religion. The cause of the chaotic condition lies in the differences among the religions and finds its origin in the animosity and hatred existing between sects and denominations. The materialists have availed themselves of this dissension amongst the religions and are constantly attacking them, intending to uproot the tree of divine planting. Owing to strife and contention among themselves, the religions are being weakened and vanquished. If a commander is at variance with his army in the execution of military tactics, there is no doubt he will be defeated by the enemy. Today the religions are at variance; enmity, strife and recrimination prevail among them; they refuse to associate; nay, rather, if necessary they shed each other’s blood. Read history and record to see what dreadful events have happened in the name of religion ….
Imitation destroys the foundation of religion, extinguishes the spirituality of the human world, transforms heavenly illumination into darkness and deprives man of the knowledge of God. It is the cause of the victory of materialism and infidelity over religion; it is the denial of Divinity and the law of revelation; it refuses Prophethood and rejects the Kingdom of God. When materialists subject imitations to the intellectual analysis of reason, they find them to be mere superstitions; therefore, they deny religion. – Ibid., p. 161.
Baha’u’llah carefully distinguished between true religion, as revealed by the messengers of God, and religious superstition, which is the product of human ignorance and corruption. The latter is the very antithesis of reason, whereas true religion is rational and in harmony with science. Abdu’l-Baha explained:
Among other principles of Baha’u’llah’s teachings was the harmony of science and religion. Religion must stand the analysis of reason. It must agree with scientific fact and proof so that science will sanction religion and religion fortify science. Both are indissolubly welded and joined in reality. If statements and teachings of religion are found to be unreasonable and contrary to science, they are outcomes of superstition and imagination. Innumerable doctrines and beliefs of this character have arisen in the past ages. Consider the superstitions and mythology of the Romans, Greeks and Egyptians; all were contrary to religion and science. It is now evident that the beliefs of these nations were superstitions, but in those times they held to them most tenaciously …. Therefore, we must cast aside such beliefs and investigate reality. That which is found to be real and conformable to reason must be accepted, and whatever science and reason cannot support must be rejected as imitation and not reality. Then differences of belief will disappear. All will become as one family, one people, and the same susceptibility to the divine bounty and education will be witnessed among mankind. – Ibid., pp. 175-176.