A seed, also known as a mnemonic phrase, is what you will use to recover your Universal Wallet if your phone is ever lost or stolen, or when you decide to upgrade to a new device. It is vital that you keep this 24-word phrase secret and secure. It will only be displayed once when you create a Universal Wallet, and it will never be stored on your device.
A private key is essentially a unique cryptographic password that gives the owner of a wallet access to the assets inside. Each wallet has its own unique private key. With the Universal Wallet, your private keys are encrypted and nobody, aside from the owner of that wallet, has access to using them. At Ethos, we talk a lot about the empowering idea of “self-custody”, this can only be achieved when you have complete control of your private keys, and in turn your assets!
In short, your private keys grant you access to the assets in each wallet, while the seed allows you to restore a copy of your private keys on a new device.