Wallet password adds an extra layer to encrypt and protect your wallet, which is required for import, transfer, staking, trading, and all operations related to your assets security. Unlike mnemonic words or passphrases, it can be modified accordingly.
ViaWallet is a decentralized wallet, unlike storing user's data on the server which can be seen in the centralized wallet, you‘ll have full access to your own data offline stored on your devices. If you lost it, ViaWallet is unable to find or reset it for you, you'll have the options to import the mnemonic words first then reset it manually.