What advice does uncle Axel give David in The Chrysalids by John Wyndham and why was it good advice?

Uncle Axel advises David to keep his abilities a secret in order to protect himself from persecution. This advice is good because in their society, anyone displaying deviations from the norm is seen as a threat and is often killed or banished. By keeping his telepathic abilities hidden, David can avoid being targeted and potentially stay safe.