By His Divine Grace A. C. Bhaktivedanta Swami Prabhupada
A person who happens to take birth in the family of a Brahman but is not qualified enough to be called a Brahmin is addressed as the relative of a Brahmin (brahma-bandhu) and not as a Brahmin. The son of a High court judge is not virtually a high court judge but there is no harm to address a high court judge’s son, as a relative of the Hon. Justice. Therefore, as by birth only one does not become a high court judge, so also one does not become a Brahmin simply by birth right but by acquiring the necessary qualifications of a Brahmin. As the high court judgeship is a post for the qualified man so also the post of a Brahmin is attainable by qualification only. The Shastra enjoins that even if such good qualifications are seen in a person born in a family of other than that of a Brahmin, the qualified man has to be accepted as a Brahmin and similarly if a person born in the family of a Brahmin, is void of brahminical qualification, then he must be treated as a non-Brahmin or in better terms a relative of a Brahmin! Lord Sri Krishna the Supreme Authority of all religious principles of the Vedas, has personally pointed out this differences.
[The Bhaktivedanta Purport to Srimad Bhagavatam 1.7.35]