The Cumaean Sibyl
The Church on Non-Christian Philosophy and Religion as a Preparation for the Gospel (outline by R. Fastiggi)
In Vatican II’s Lumen gentium, 16, we are told that, ”whatever good or truth is found among [non-Christians] is looked upon by the Church as a preparation for the Gospel.”
The following is a rough chronology of some views of the Catholic Church on this topic.
Mt 2:1 The Magi from the East [they might have been Persian Zoroastrian priests].
Acts 17:22-32 Paul at the Areopagus recognizes that the Athenians are “very respectful of the gods” (deisidaimonesterous) [trans. as “very religious” in RSV and NAB].
St. Justin Martyr (c.100- 165 affirms that the “seed of the Logos (sperma logou) is “implanted in every race of men” [Second Apology, chap. 8]. He also believes that the Non-Christian philosophies contain the “seminal Word” (logos spermatikos) [Second Apology, chap. 13]. Vatican II’s Decree on the Missionary Activity of the Church (Ad gentes), no. 11 , extends St. Justin’s metaphor to non-Christian religions, which contain “seeds of the Word” (semina Verbi). Pope Paul VI, in his 1975 Apostolic Exhortation, Evangelii nuntiandi, 53, likewise states that non-Christian religions “are all impregnated with innumerable seeds of the Word (semina Verbi).
Clement of Alexandria (c. 150-215) speaks of pagan philosophy as a “schoolmaster” to bring Greeks to Christ (Stromata I, 5).
Augustine (354-430); “The Truth, wherever it is found, is His [the Lord’s]” De doctrina Christina, book 2, 18, 28.
Pope Gregory VII, 1076, writes to the King of Morocco (Letters, book 3, n. 21 PL 148, 151: “We believe in and confess one God, though in a different manner, who, as Creator of the ages and Governor of the world, we praise and honor every day” (“unum Deum, licet diverso modo, credimus et confitemur, qui cum Creatorem saeculorum et gubernatorem huius mundi quotidie laudamus et veneramur..”) [cited in a footnote to Vatican II’s Declaration on the Relation of the Church to Non Christian Religions, Nostra aetate, 2 
Lateran IV (1215): “The Holy Spirit gave…the doctrine of salvation to the human race, first through Moses and the holy prophets and through his other servants” (Denz-H. 800).
Cardinal Nicholas of Cusa (1401-1464) is called the theologian of the concordantia religionum because of his work, De pace fidei, seeking peaceful terms with all faiths. In Cribratio Alcorani I, 6: (the Sifting of the Qur’an), Nicholas writes: “If anything beautiful, true and clear is found in the Qur’an, by necessity, it is a ray of the most luminous Gospel.”
Marsilio Ficino (1433-1466)—believed that Platonism was, at least in part, divinely inspired because of its affirmation of the immortality of the soul.
The Sistine Chapel: Pope Sixtus IV (r.1471-1484), completed under Julius II (1503-13) shows sibyls pointing to Christ.
Matteo Ricci, S.J. (c. 1552- 1611), missionary to China, shows respect for Confucius and Chinese culture.
Roberto de Nobili, S.J.(1577-1656) – dressed as a Hindu ascetic and put on his forehead the sandalwood paste used by the Brahmins. His methods were defended by Pope Gregory XV (1621-23). Cf. Fr. John Laux, Church History (1945, reprinted 1989 by Tan Books), p. 469.
Yves de Paris, OFMCap. (1588-1678): “And even if some people are so criminal as to be carried to sacrilegious adorations, it must be admitted that they all have in their hearts this same impression of nature to adore God; and if the ways in themselves are profane, the first motive and initial impulse are holy” (La théologie naturelle. [TN] book 1, p. 3).
“God does not hold so much rigor against the infidel peoples; His goodness exceeds their demerits; and all the doctors remain in agreement that if the barbarians observe well the natural law, if they cooperate with the graces which the divine mercy offers them, then they will receive the particular instructions of the faith necessary to their salvation” (TN, book 4 p. 2)
Francois Noel, S.J. (1651-1729) –Missionary to China, writes a book on the fundamental harmony of Chinese and Christian philosophy.
John Henry Newman (1801-1890): “The Moral Governor of the world has scattered the seeds of truth far and wide…” (Essays Critical and Historical, sec. 9, p. 431).
Pope John Paul II (1920-2005; pope from 1978-2005) recognizes that “the fundamental questions which pervade human life” are found in the sacred writings of even non-Christian religions (cf. encyclical, Fides et ratio, 1 ).
Addendum on 1 Cor 10:14-22: In this passage, Paul urges the Corinthians “to shun the worship of idols” (v. 14) because “what the pagans sacrifice they offer to demons and not to God” (v. 20). Some have used this passage to argue that all non-Christian worship (with the exception of Judaism) is directed towards the Devil or demons and not towards the true God. This passage, though, is concerned with “the worship of idols” connected to certain polytheistic, sacrificial religions in Corinth at that time. It is not proper to go from a particular condemnation to a universal application. While it might be true that demons are involved in some polytheistic cults of today, it is important to do an objective study of a non-Christian religion’s concept of God before applying Paul’s warning about idolatry found in 1 Cor 10:14-22. Moreover, it is important to balance 1 Cor 14:22 with other scriptural passages such as Rom 1:19-21 and Acts 17:22-28 where Paul states that the Gentiles have knowledge of the one true God.