Complex sentence: As for any antenna system, efficient electrical coupling requires impedance matching since the large (resistive) impedance seen across the small loop when tuned with a parallel capacitor will not be a good match to a standard transmission line or transmitter.
Split into simpler sentences: As for any antenna system, efficient electrical coupling requires impedance matching. For a small loop tuned with a parallel capacitor the resulting large (resistive) impedance (or for a small loop tuned with a series capacitor the resulting small impedance) will not be a good match to a standard transmission line or transmitter.