The inductive effect - I ("electron withdrawing effect") makes that a substituent "sucks" part of the electrons from the rest of the organic molecule where it is attached. The inductive effect + I ("electron donating effect") makes that a substituent "pumps" electrons partially in the rest of the organic molecule where it is attached.
The greater electronegativity of chlorine than that of carbon partially draws electrons from the C-Cl bond
The greater electronegativity of carbon than that of hydrogen gives a slight excess of negative charge at the carbon which partially pushes the electrons of the C-C bond into the rest of molecule.