A public key is the sending & receiving address of a blockchain wallet. Think of it as your wallet’s unique “mailing address.” The public key is absolutely necessary to know when you go to send or receive digital assets.
In contrast, the private key of a blockchain wallet is the “master key” that allows someone to access all the functionality of a wallet. It allows someone to restore their wallet from one wallet provider to another. It is important for wallet holders to retain full control of his/her private keys, just like one would do with a password. An easy phrase to remember: “not your (private) keys, not your coins.”