Electret Microphone cannot recognize human voice
The eletret microphone requires a dc bias to enable it to function. However, you only need to detect the audio (ac) signal to amplify and feed to a speaker. The capacitor blocks the dc bias, whilst passing the audio signal to the amplifier. There must be an amplifier to generate the required power to drive the speaker. The speaker will have a low impedance, typically  8 to 16 ohms. The amplifier must provide the power and a matching output impedance _ else won't work!