Narsinh Mehta, the fifteenth century poet of Junagadh honoured as the first poet of Gujarati, answered the question in his hymn's first line, call that one a Vaishnava who knows the pain of others. The verses that follow build the portrait. The true devotee helps the suffering without letting pride enter the mind, honours everyone and speaks ill of no one, keeps truth in speech and never touches another's wealth, is free of desire and deceit, has renounced greed and lust, and sees all women other than his wife as his mother. Such a person, the hymn ends, sanctifies their whole lineage. What is startling is what the hymn does not say.
There is no mention of temple, image, pilgrimage, fast or ritual competence, the standard markers of religious identity in Mehta's world or any other. The definition is entirely ethical, devotion measured by compassion, and it belongs to the wider bhakti insistence that God is reached through love and character rather than status, a current Mehta shared with the sant poets across India. Mehta's own life, as tradition tells it, enacted the point, a Brahmin who sang among those his caste world excluded and was ostracized for it. The hymn compresses that stance into a dozen lines simple enough for a child, which is how it has been transmitted ever since.