A theory of excitations in liquid helium is developed from the first principle in connection with the new spectrum discovered by Cowley and Woods. In deriving the results a crude estimate has to be done due to computational difficulties. This paper is, therefore, limited to a qualitative theory. Gross structure of two branches of excitation is obtained; one of them is interpreted as a resonance spectrum of particle-particle scattering, while the other corresponds to the phonon-roton spectrum. Physical background of the existence of the resonance branch is discussed from the point of view of the Bose condensation of liquid helium.