Is the resonator a frequency sensitive device or is it a signal source? I believe its the former but why does a transistor need a resonator to operate as an oscillator (A resonator is just selecting a frequency, its not producing oscillation by itself)?
A parallel oscillator just has the highest impedance at its resonant frequency. How can it make the transistor oscillate at the same frequency (where is the signal coming from in an otherwise "DC" circuit)?
An oscillator is technically amplifier with positive feedback. There must be matched certain conditions regarding to phase shift and amplification to work. Role of resonator is to set working frequency of oscillator. Check this: http://jacquesricher.com/NEETS/ (modules 8 and 9)
As you said, the resonator has the highest impedance at resonating frequency, therefore the signals with this frequency are amplified all others are cut-off. The signal of right frequency comes out from noise and from turn-on transient, at that time there is a presence of all frequencies from zero to the infinity.
