Criticism of religion must extend not only to its basic claims but to all of its statements. Religion is liable to distortion from without and to corruption from within. Since it frequently absorbs ideas not indigenous to its spirit, it is necessary to distinguish between the authentic and the spurious. Furthermore, superstition, pride, self-righteousness, bias, and vulgarity, may defile the finest traditions. Faith in its zeal tends to become bigotry. The criticism of reason, the challenge, and the doubts of the unbeliever may, therefore, be more helpful to the integrity of faith than the simple reliance on one's own faith.