The energy functional of ideal magnetohydrodynamics (MHD) is extended to the regime of finite resistivity and transformed to an intuitive form, which separates pressure-gradient, current-density drive and stabilizing phenomena, analogously to the ideal version of the functional derived by Johnson and Greene. The resulting resistive energy functional is not in the form of a solvable eigenvalue problem but is intended to analyze the energetic composition of eigenfunctions which were calculated in advance by solving the MHD equations. The new resistive energy functional provides information on the different energetic drives and stabilizing phenomena of an eigenfunction. The new energy functional has been implemented in the CASTOR3D code in general 3D curvilinear coordinates and successfully validated across three different coordinate systems for a numerical test case.