Bahá’u’lláh wrote:

“The Great Being saith: O ye children of men! The fundamental purpose animating the Faith of God and His Religion is to safeguard the interests and promote the unity of the human race, and to foster the spirit of love and fellowship amongst men. Suffer it not to become a source of dissension and discord, of hate and enmity…”
(Gleanings from the Writings of Bahá’u’lláh, p. 215)

“The purpose of religion as revealed from the heaven of God’s holy Will is to establish unity and concord amongst the peoples of the world; make it not the cause of dissension and strife…”
(Tablets of Bahá’u’lláh, p. 129)

“…The well-being of mankind, its peace and security, are unattainable unless and until its unity is firmly established. This unity can never be achieved so long as the counsels which the Pen of the Most High hath revealed are suffered to pass unheeded.”
(Gleanings from the Writings of Bahá’u’lláh, p. 286)

“It is permitted that the peoples and kindreds of the world associate with one another with joy and radiance. O people!  Consort with the followers of all religions in a spirit of friendliness and fellowship…”
(Tablets of Bahá’u’lláh, p. 22)

“In former religions such ordinances as…the ban on association and companionship with other peoples…had been laid down and affirmed according to the exigencies of the time; however, in this mighty Revelation…His infallible decree hath prescribed that which We have set forth above.”
(Tablets of Bahá’u’lláh, p. 28)