Why are the keys so important?
Your public key is presented by your address in the blockchain network. Anyone can send you crypto using this address. However, knowing the address is not enough to manage the funds on it. In order to send the funds to another address, you’ll need to sign the transaction with the private key. This makes the keys, and the private key in particular, the main object of any cryptocurrency system, from the standpoint of development.
The need to match each public key with its private key and store all these pieces of information is now eliminated with the help of the seed phrase (or mnemonic phrase). If you have access to the seed phrase, you can manage the funds.