The resonant tunneling transmission of an electron through the quantum wire comprising two three-dimensional δ-potentials located along the nanotube axis is considered. Using the formulas obtained recently for amplitudes of multichannel scattering, the condition (equation) of resonance is found for the multichannel scattering, at which the system under consideration becomes completely transparent for motion of the electron. A procedure based on the method of vector diagrams is proposed for simplification of the resonance equation. It is shown that if the initial energy of longitudinal motion is insufficient for excitation of new scattering channels, then the resonance equation coincides with the corresponding equation of one-dimensional problem.