"… Thou hadst asked some questions; that why the blessed and spiritual souls, who are firm and steadfast, shun the company of degenerate persons. This is because, that just as the bodily diseases like consumption and cancer are contagious, likewise the spiritual diseases are also infectious. If a consumptive should associate with a thousand safe and healthy persons, the safety and health of these thousand persons would not affect the consumptive and would not cure him of his consumption. But when this consumptive associates with those thousand souls, in a short time the disease of consumption will infect a number of those healthy persons. This is a clear and self-evident question."

(‘Abdu’l-Bahá: Tablet to an individual believer, October 1921: Star of the West, Vol. XII, No. 14, p. 233)?

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