Buying Eth: No investment in a common enterprise, no expectation of profit nor is that non-profit derived from others. Not a security.
Staking Eth: Investment in common enterprise, expectation of profit and profit derived from others. Looks and quacks like a security.
Buying and holding Eth without staking it shouldn't be considered a security, while staking said Eth should be considered a security. At least if we're still following the "Howey Test".