When we are on the material platform, there are different types of religions—Hinduism, Christianity, Islam, Buddhism and so on. These are instituted for a particular time, a particular country or a particular person. Consequently there are differences. Christian principles are different from Hindu principles, and Hindu principles are different from Muslim and Buddhist principles. These may be considered on the material platform, but when we come to the platform of transcendental devotional service, there are no such considerations. The transcendental service of the Lord (sādhana-bhakti) is above these principles. The world is anxious for religious unity, and that common platform can be achieved in transcendental devotional service. This is the verdict of Śrī Caitanya Mahāprabhu. When one becomes a Vaiṣṇava, he becomes transcendental to all these limited considerations.
This is confirmed by Lord Kṛṣṇa in the Bhagavad-gītā ( BG 14.26):
māṁ ca yo ‘vyabhicāreṇa bhakti-yogena sevate sa guṇān samatītyaitān brahma-bhūyāya kalpate
“One who engages in full devotional service, unfailing in all circumstances, at once transcends the modes of material nature and thus comes to the level of Brahman.” The devotional activities of the Kṛṣṇa consciousness movement are completely transcendental to material considerations. As far as different faiths are concerned, religions may be of different types, but on the spiritual platform, everyone has an equal right to execute devotional service.
(Srila Prabhupada, CC Madhya 25.121, Purport)